Conjugated diene-based polymer, branching agent, production method for conjugated diene-based polymer, extended conjugated diene-based polymer, rubber composition, and tire

ABSTRACT

A conjugated diene-based polymer of the present invention has an absolute molecular weight measured by viscosity detector-equipped GPC-light scattering measurement, of 40×104 or more and 5000×104 or less, has a branching number (Bn) measured by the viscosity detector-equipped GPC-light scattering measurement, of 8 or more, and has a modification ratio of 60% by mass or more.

TECHNICAL FIELD

The present invention relates to a conjugated diene-based polymer, abranching agent, a production method for a conjugated diene-basedpolymer, an extended conjugated diene-based polymer, a rubbercomposition, and a tire.

BACKGROUND ART

There have been increasing demands for reduction of fuel consumption invehicles, and improvement of materials of a vehicle tire, particularly,of a tire tread in contact with the ground is required.

Recently, development of a material having low rolling resistance,namely, having a low hysteresis loss property, has been demanded.

Besides, in order to reduce the weight of a tire, it is necessary toreduce the thickness of a tread portion of the tire, and there is ademand also for a material having high abrasion resistance.

On the other hand, a material used for a tire tread is required, fromthe viewpoint of safety, to be excellent in wet skid resistance and havepractically sufficient fracture performance.

An example of a rubber material meeting the aforementioned requirementsincludes a rubber material containing a rubber-like polymer and areinforcing filler such as carbon black or silica.

When a rubber material containing silica is used, balance between a lowhysteresis loss property and wet skid resistance can be improved.Besides, an attempt has been made to reduce a hysteresis loss byimproving dispersibility of silica in a rubber material throughintroduction of a functional group having affinity or reactivity withsilica into a molecular end of a rubber-like polymer having highmobility, and further by reducing the mobility of the molecular end ofthe rubber-like polymer through a bond to a silica particle.

For example, Patent Documents 1 to 3 propose a composition of a modifiedconjugated diene-based polymer obtained by reacting an alkoxysilanehaving an amino group with a conjugated diene-based polymer active end,and silica.

Besides, Patent Document 4 proposes a modified conjugated diene-basedpolymer obtained by a coupling reaction of a polymer active end and apolyfunctional silane compound.

List of Prior Art Documents Patent Document

-   Patent Document 1: Japanese Patent Laid-Open No. 2005-290355-   Patent Document 2: Japanese Patent Laid-Open No. 11-189616-   Patent Document 3: Japanese Patent Laid-Open No. 2003-171418-   Patent Document 4: International Publication No. WO07/114203

SUMMARY OF INVENTION Problems to be Solved by Invention

Silica has, however, a disadvantage of being inferior in dispersibilityin a composition to carbon black because it has a hydrophilic surfaceand hence has low affinity with a conjugated diene-based polymer whilecarbon black has a hydrophobic surface. Therefore, a compositioncontaining silica needs to additionally contain a silane modifier or thelike to improve the dispersibility of silica in the composition byimparting a bond between the silica and the conjugated diene-basedpolymer.

Besides, when a functional group having high reactivity with silica isintroduced into a molecular end of the conjugated diene-based polymer,there is a problem that processability tends to be degraded, forexample, it becomes difficult to knead because a reaction with a silicaparticle proceeds during kneading process to increase the viscosity of aresultant composition, or surface coarseness or sheet breakage is easilycaused when formed into a sheet after the kneading.

In addition, when such a composition is used to obtain a vulcanizate, inparticular, used to obtain a vulcanizate containing an inorganic fillersuch as silica, it has a problem that the balance between a lowhysteresis loss property and wet skid resistance, and abrasionresistance are not sufficient.

Therefore, an object of the present invention is to provide a conjugateddiene-based polymer that is extremely excellent in processabilityobtained when used for obtaining a vulcanizate, and when in the form ofa vulcanizate, is excellent in balance between a low hysteresis lossproperty and wet skid resistance and in abrasion resistance, and haspractically sufficient fracture performance.

Means for Solving Problems

The present inventors have studied earnestly to solve theabove-described problems of the related arts, consequently found that aconjugated diene-based polymer having an absolute molecular weightfalling in a prescribed range, and having a branch number (Bn) fallingin a specific range is extremely excellent in processability obtainedwhen used for obtaining a vulcanizate, and when in the form of avulcanizate, is excellent in balance between a low hysteresis lossproperty and wet skid resistance and in abrasion resistance, and haspractically sufficient fracture performance, and completed the presentinvention.

Specifically, the present invention provides the following:

[1] A conjugated diene-based polymer having an absolute molecular weightmeasured by viscosity detector-equipped GPC-light scatteringmeasurement, of 40×10⁴ or more and 5000×10⁴ or less, and having abranching number (Bn) measured by the viscosity detector-equippedGPC-light scattering measurement, of 8 or more.

[2] The conjugated diene-based polymer according to [1] above, having amodification ratio of 60% by mass or more.

[3] The conjugated diene-based polymer according to [1] or [2] above,wherein the conjugated diene-based polymer has a star polymer structurehaving 3 or more branches, wherein

at least one branched chain of the star structure comprises a portionderived from a vinyl-based monomer containing an alkoxysilyl group or ahalosilyl group, and

the portion derived from the vinyl-based monomer containing thealkoxysilyl group or the halosilyl group further comprises a main chainbranch structure.

[4] The conjugated diene-based polymer according to any one of [1] to[3] above, wherein

the portion derived from the vinyl-based monomer containing thealkoxysilyl group or the halosilyl group is a monomer unit based on acompound represented by the following formula (1) or (2), and contains abranch point of a polymer chain containing the monomer unit based on thecompound represented by the formula (1) or (2), and

at least one end of the conjugated diene-based polymer is coupled byusing a coupling agent:

wherein in the formula (1), R¹ represents a hydrogen atom, an alkylgroup having 1 to 20 carbon atoms, or an aryl group having 6 to 20carbon atoms, and may have a branch structure in a part thereof;

R² and R³ each independently represent an alkyl group having 1 to 20carbon atoms, or an aryl group having 6 to 20 carbon atoms, and may havea branch structure in a part thereof;

each of R¹ to R³, if present in a plural number, is respectivelyindependent;

X¹ represents an independent halogen atom;

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3;

in the formula (2), R² to R⁵ each independently represent an alkyl grouphaving 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbonatoms, and may have a branch structure in a part thereof, and each of R²to R⁵, if present in a plural number, is respectively independent;

X² and X³ represent an independent halogen atom;

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3; and

a represents an integer of 0 to 2, b represents an integer of 0 to 3, crepresents an integer of 0 to 3, and (a+b+c) is 3.

[5] The conjugated diene-based polymer according to [4] above,containing a monomer unit based on a compound represented by the formula(1) wherein R¹ is a hydrogen atom, and m is 0.

[6] The conjugated diene-based polymer according to [4] above,containing a monomer unit based on a compound represented by the formula(2) wherein m is 0 and b is 0.

[7] The conjugated diene-based polymer according to [4] above,containing a monomer unit based on a compound represented by the formula(1) wherein R¹ is a hydrogen atom, m is 0, and 1 is 0.

[8] The conjugated diene-based polymer according to [4] above,containing a monomer unit based on a compound represented by the formula(2) wherein m is 0, 1 is 0, a is 0, and b is 0.

[9] The conjugated diene-based polymer according to [4] above,containing a monomer unit based on a compound represented by the formula(1) wherein R¹ is a hydrogen atom, 1 is 0, and n is 3.

[10] A branching agent for the conjugated diene-based polymer accordingto [4] above, wherein the branching agent is a compound represented bythe following formula (1) or (2):

wherein in the formula (1), R¹ represents a hydrogen atom, an alkylgroup having 1 to 20 carbon atoms, or an aryl group having 6 to 20carbon atoms, and may have a branch structure in a part thereof;

R² and R³ each independently represent an alkyl group having 1 to 20carbon atoms, or an aryl group having 6 to 20 carbon atoms, and may havea branch structure in a part thereof;

each of R¹ to R³, if present in a plural number, is respectivelyindependent;

X¹ represents an independent halogen atom;

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3;

in the formula (2), R² to R⁵ each independently represent an alkyl grouphaving 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbonatoms, and may have a branch structure in a part thereof, and each of R²to R⁵, if present in a plural number, is respectively independent;

X² and X³ represent an independent halogen atom;

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3; and

a represents an integer of 0 to 2, b represents an integer of 0 to 3, crepresents an integer of 0 to 3, and (a+b+c) is 3.

[11] The branching agent according to [10] above, wherein the branchingagent is a compound represented by the formula (1) wherein R¹ is ahydrogen atom and m is 0.

[12] The branching agent according to [10] above, wherein the branchingagent is a compound represented by the formula (2) wherein m is 0, and bis 0.

[13] The branching agent according to [10] above, wherein the branchingagent is a compound represented by the formula (1) wherein R¹ is ahydrogen atom, m is 0, and 1 is 0.

[14] The branching agent according to [10] above, wherein the branchingagent is a compound represented by the formula (2) wherein m is 0, 1 is0, a is 0, and b is 0.

[15] The branching agent according to [10] above, wherein the branchingagent is a compound represented by the formula (1) wherein R¹ is ahydrogen atom, 1 is 0, and n is 3.

[16] A method for producing the conjugated diene-based polymer accordingto any one of [1] to [9] above, comprising:

a polymerizing/branching step of polymerizing at least a conjugateddiene compound in the presence of an organic lithium-based compound toobtain a conjugated diene-based polymer having a main chain branchstructure by using the branching agent according to any one of [10] to[15] above; and

a step of coupling the conjugated diene-based polymer by using acoupling agent, and/or a step of modifying the conjugated diene-basedpolymer with a modifier having a nitrogen atom-containing group.

[17] The method for producing the conjugated diene-based polymeraccording to [16] above, wherein the modifier contains a modifierrepresented by any one of the following general formulas (A) to (C):

wherein R¹ to R⁴ each independently represent an alkyl group having 1 to20 carbon atoms or an aryl group having 6 to 20 carbon atoms, R⁵represents an alkylene group having 1 to 10 carbon atoms, R⁶ representsan alkylene group having 1 to 20 carbon atoms,

m represents an integer of 1 or 2, n represents an integer of 2 or 3,(m+n) is an integer of 4 or more, and each of R¹ to R⁴, if present in aplural number, is respectively independent.

wherein R¹ to R⁶ each independently represent an alkyl group having 1 to20 carbon atoms or an aryl group having 6 to 20 carbon atoms, R⁷ to R⁹each independently represent an alkylene group having 1 to 20 carbonatoms,

m, n, and 1 each independently represent an integer of 1 to 3, (m+n+1)is an integer of 4 or more, and each of R¹ to R⁶, if present in a pluralnumber, is respectively independent.

wherein R¹² to R¹⁴ each independently represent a single bond or analkylene group having 1 to 20 carbon atoms, R¹⁵ to R¹⁹ and R²⁰ eachindependently represent an alkyl group having 1 to 20 carbon atoms, R¹⁹and R²² each independently represent an alkylene group having 1 to 20carbon atoms, R²¹ represents an alkyl group or a trialkyl silyl grouphaving 1 to 20 carbon atoms,

m represents an integer of 1 to 3, p represents 1 or 2,

each of R¹² to R²², m and p, if present in a plural number, isrespectively independent, and may be the same or different,

i represents an integer of 0 to 6, j represents an integer of 0 to 6, krepresents an integer of 0 to 6, (i+j+k) is an integer of 4 to 10, and

A represents a hydrocarbon group having 1 to 20 carbon atoms, or anorganic group having at least one atom selected from the groupconsisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfuratom, and a phosphorus atom, and not having active hydrogen.

[18] The production method for the conjugated diene-based polymeraccording to [17] above, wherein A is represented by any one of thefollowing general formulas (II) to (V) in the formula (C):

wherein B¹ represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, a represents an integer of 1 to 10, and B¹, if presentin a plural number, is respectively independent;

wherein B² represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, B³ represents an alkyl group having 1 to 20 carbonatoms, a represents an integer of 1 to 10, and each of B² and B³, ifpresent in a plural number, is respectively independent;

wherein B⁴ represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, a represents an integer of 1 to 10, and B⁴, if presentin a plural number, is respectively independent; and

wherein B⁵ represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, a represents an integer of 1 to 10, and B⁵, if presentin a plural number, is respectively independent.

[19] An extended conjugated diene-based polymer comprising:

100 parts by mass of the conjugated diene-based polymer according to anyone of [1] to [9] above; and

1 to 60 parts by mass of at least one selected from the group consistingof an extender oil, a liquid rubber, and a resin.

[20] A rubber composition comprising:

a rubber component; and

5.0 parts by mass or more and 150 parts by mass or less of a fillerbased on 100 parts by mass of the rubber component,

wherein the rubber component contains, based on a total amount of therubber component, 10% by mass or more of the conjugated diene-basedpolymer according to any one of [1] to [9] above, or the extendedconjugated diene-based polymer according to [19] above.

[21] A tire comprising the rubber composition according to [20] above.

Advantages of Invention

According to the present invention, a conjugated diene-based polymerthat is extremely excellent in processability obtained when used forobtaining a vulcanizate, and when in the form of a vulcanizate, canrealize excellent balance between a low hysteresis loss property and wetskid resistance, has high abrasion resistance, and has practicallysufficient fracture performance can be obtained.

MODE FOR CARRYING OUT INVENTION

Now, an embodiment for practicing the present invention (hereinafterreferred to as the “present embodiment”) will be described in detail.

It is noted that the following present embodiment is merely an examplefor describing the present invention and the present invention is notlimited to the following description but may be variously modifiedwithin the scope thereof.

[Conjugated Diene-Based Polymer]

A conjugated diene-based polymer of the present embodiment has anabsolute molecular weight, obtained by viscosity detector-equippedGPC-light scattering measurement, of 40×10⁴ or more and 5000×10⁴ orless, and a branch number (Bn), obtained by the viscositydetector-equipped GPC-light scattering measurement, of 8 or more.

A conjugated diene-based polymer specified in the absolute molecularweight and the branch number as described above is extremely excellentin processability obtained when used for obtaining a vulcanizate, andwhen in the form of a vulcanizate, is excellent in balance between a lowhysteresis loss property and wet skid resistance and in abrasionresistance, and has practically sufficient fracture performance.

The conjugated diene-based polymer of the present embodiment has amodification ratio of preferably 60% by mass or more.

A modified conjugated diene-based polymer specified in the absolutemolecular weight, the branch number and the modification ratio asdescribed above is extremely excellent in processability obtained whenused for obtaining a vulcanizate, and when in the form of a vulcanizate,is particularly excellent in balance between a low hysteresis lossproperty and wet skid resistance, and has excellent abrasion resistanceand practically sufficient fracture performance.

It is noted that the “conjugated diene-based polymer” herein encompassesa modified conjugated diene-based polymer obtained after modificationunless otherwise stated.

(Absolute Molecular Weight)

From the viewpoints of processability, balance between a low hysteresisloss property and wet skid resistance, abrasion resistance, and fractureperformance, the conjugated diene-based polymer of the presentembodiment has an absolute molecular weight, obtained by viscositydetector-equipped GPC-light scattering measurement, of 40×10⁴ or moreand 5000×10⁴ or less.

In general, a polymer having a branch structure tends to have a smallermolecule when compared with a straight-chain polymer having the samemolecular weight. Therefore, in employing a molecular weight in terms ofpolystyrene obtained by gel permeation chromatography (GPC), which isrelative comparison with a standard polystyrene sample for screening apolymer in accordance with the size of a molecule, the molecular weightof a polymer having a branch structure tends to be underestimated.

On the other hand, as for an absolute molecular weight measured byviscosity detector-equipped GPC-light scattering measurement, amolecular weight (absolute molecular weight) is measured by directlyobserving the size of a molecule by a light scattering method, andhence, as compared with a molecular weight in terms of polystyreneobtained by gel permeation chromatography (GPC), is not affected by astructure of the polymer or interaction with a column filler. Therefore,the molecular weight can be accurately measured without being affectedby a polymer structure such as a branch structure of a conjugateddiene-based polymer.

The absolute molecular weight of the conjugated diene-based polymer ofthe present embodiment is 40×10⁴ or more, preferably 50×10⁴ or more,more preferably 60×10⁴ or more, further preferably 80×10⁴ or more, andstill further preferably 100×10⁴ or more.

The absolute molecular weight of the conjugated diene-based polymer ofthe present embodiment is 5000×10⁴ or less, preferably 4500×10⁴ or less,more preferably 4000×10⁴ or less, further preferably 3500×10⁴ or less,and still further preferably 3000×10⁴ or less.

When the absolute molecular weight is 40×10⁴ or more, balance between alow hysteresis loss property and wet skid resistance, and abrasionresistance when in the form of a vulcanizate are excellent. When theabsolute molecular weight is 5000×10⁴ or less, processability obtainedwhen used for obtaining a vulcanizate and dispersibility of a filler areexcellent, and practically sufficient fracture performance can beobtained.

The absolute molecular weight of the conjugated diene-based polymer canbe measured by a method described in examples below.

The absolute molecular weight of the conjugated diene-based polymer ofthe present embodiment can be controlled to fall in the above-describednumerical range by adjusting an amount of a polymerization initiator tobe added, the number of functional groups of a branching agent, anamount of the branching agent to be added, timing of adding thebranching agent, and amounts of a coupling agent and a modifier to beadded.

(Branch Number)

From the viewpoints of processability, balance between a low hysteresisloss property and wet skid resistance, abrasion resistance, and fractureperformance, the branch number (Bn) of the conjugated diene-basedpolymer of the present embodiment is 8 or more.

The branch number (Bn) being 8 or more means that the conjugateddiene-based polymer of the present embodiment has 8 or more polymerchains as side chains with respect to a substantially longest polymermain chain.

The branch number (Bn) of a conjugated diene-based polymer is defined,by using a contracting factor (g′) measured by viscositydetector-equipped GPC-light scattering measurement, as g′=6Bn/{(Bn+1)(Bn+2)}.

In general, a polymer having a branch tends to have a smaller moleculewhen compared with a straight-chain polymer having the same absolutemolecular weight.

The contracting factor (g′) is an index of a size ratio occupied by amolecule in a straight-chain polymer assumed to have the same absolutemolecular weight. In other words, when the branch number of a polymer isincreased, the contracting factor (g′) tends to be reduced.

For the contracting factor, an intrinsic viscosity is used as an indexof the size of a molecule in this embodiment, and a straight-chainpolymer satisfies the relationship: intrinsic viscosity [η]=−3.883M^(0.771), wherein M represents an absolute molecular weight.

The contracting factor (g′) expresses, however, a decreasing ratio ofthe size of a molecule and does not accurately express a branchstructure of the polymer.

Therefore, the branch number (Bn) of the conjugated diene-based polymeris calculated by using a value of the contracting factor (g′) obtainedat each absolute molecular weight of the conjugated diene-based polymer.The thus calculated “branch number (Bn)” accurately expresses the numberof polymers directly or indirectly bonded to a longest main chainstructure.

The calculated branch number (Bn) can be an index expressing a branchstructure of a conjugated diene-based polymer. For example, in a general4-branched star polymer (having 4 polymer chains connected to a centerportion), two polymer chain arms are bonded to a longest highly branchedmain chain structure, and hence the branch number (Bn) is evaluated as2.

In a general 8-branched star polymer, 6 polymer chain arms are bonded toa longest highly branched main chain structure, and the branch number(Bn) is evaluated as 6.

The conjugated diene-based polymer of the present embodiment has thebranch number (Bn) of 8 or more, and such a case means that it is aconjugated diene-based polymer having, as a star polymer structure,branches similar to a 10-branched star polymer structure.

Here, a “branch” is formed by a direct or indirect bond of one polymerto another polymer. Besides, the “branch number (Bn)” corresponds to thenumber of polymers directly or indirectly bonded to a longest main chainstructure.

When the branch number (Bn) is 8 or more, the conjugated diene-basedpolymer of the present embodiment is excellent in balance between a lowhysteresis loss property and wet skid resistance when in the form of avulcanizate.

In general, increase of an absolute molecular weight tends todeteriorate processability, and when an absolute molecular weight isincreased in a straight chain polymer structure, a vulcanizate obtainedtherefrom is largely increased in the viscosity and largely deterioratedin the processability. Therefore, even when a large number of functionalgroups are introduced into the polymer to improve affinity and/orreactivity with silica to be blended as a filler, the silica cannot besufficiently dispersed in the polymer in kneading process. As a result,the function of the introduced functional groups cannot be exhibited,and hence, an originally expected effect of improving a low hysteresisloss property and wet skid resistance by the introduction of thefunctional groups cannot be exhibited.

On the other hand, since the conjugated diene-based polymer of thepresent embodiment is specified to have a branch number (Bn) of 8 ormore, the increase of the viscosity of a vulcanizate obtained therefromdue to increase of the absolute molecular weight is largely suppressed,and hence the polymer can be sufficiently mixed with silica or the likein the kneading process, so that the silica can be dispersed around theconjugated diene-based polymer. As a result, abrasion resistance andfracture performance can be improved by setting a molecular weight ofthe conjugated diene-based polymer to be high, and in addition, silicacan be dispersed around the polymer by sufficient kneading so as to makefunctional groups to act and/or react, and thus, the polymer can attainpractically sufficient low hysteresis loss property and wet skidresistance.

The absolute molecular weight of the conjugated diene-based polymer canbe measured by a method described in the examples below.

The branch number (Bn) of the conjugated diene-based polymer of thepresent embodiment is 8 or more, preferably 10 or more, more preferably12 or more, and further preferably 15 or more.

A conjugated diene-based polymer having a branch number (Bn) falling inthis range tends to be excellent in processability obtained when usedfor obtaining a vulcanizate.

The upper limit of the branch number (Bn) is not especially limited, andmay be equal to or larger than a detection limit, and is preferably 84or less, more preferably 80 or less, further preferably 64 or less, andstill further preferably 57 or less.

If the branch number is 84 or less, abrasion resistance obtained whenused for obtaining a vulcanizate tends to be excellent.

The branch number of the conjugated diene-based polymer can becontrolled to be 8 or more in accordance with a combination of an amountof a branching agent to be added and an amount of an end modifier to beadded. Specifically, the branch number can be controlled in accordancewith the number of functional groups of a branching agent, an amount ofthe branching agent to be added, timing of adding the branching agent,and an amount of a modifier to be added. More specific description willbe given in [Production Method for Conjugated Diene-based Polymer]described below.

(Modification Ratio)

From the viewpoints of processability, balance between a low hysteresisloss property and wet skid resistance, abrasion resistance, and fractureperformance, the conjugated diene-based polymer of the presentembodiment preferably has a modification ratio of 60% by mass or morebased on a total amount of conjugated diene-based polymers.

Herein, the term “modification ratio” refers to a mass ratio of aconjugated diene-based polymer having a nitrogen-containing functionalgroup to a total amount of conjugated diene-based polymers.

For example, assuming that a nitrogen-containing modifier is reactedwith a terminal end, a mass ratio of a conjugated diene-based polymerhaving a nitrogen-containing functional group owing to thenitrogen-containing modifier to a total amount of conjugated diene-basedpolymers is expressed as a modification ratio.

On the other hand, also when a polymer is branched by using a branchingagent containing nitrogen, the thus generated conjugated diene-basedpolymer has a nitrogen-containing functional group, and such a branchedpolymer is also counted in calculation of a modification ratio.

In other words, herein, when a conjugated diene-based polymer isparticularly a “modified conjugated diene-based polymer” having beenmodified, a mass ratio of a sum of a coupling polymer obtained by usinga modifier having a nitrogen-containing functional group and/or abranched polymer obtained by using a branching agent having anitrogen-containing functional group corresponds to the modificationratio.

The modification ratio is preferably 65% by mass or more, morepreferably 70% by mass or more, further preferably 75% by mass or more,still further preferably 80% by mass or more, and much furtherpreferably 82% by mass or more.

If the modification ratio is 60% by mass or more, the resultant polymertends to be excellent in processability obtained when used for obtaininga vulcanizate, and be more excellent in abrasion resistance and a lowhysteresis loss property when in the form of a vulcanizate.

The modification ratio can be measured by chromatography capable ofseparating a functional group-containing modified component and anon-modified component.

As a method using chromatography, a method using a column for gelpermeation chromatography using, as a filler, a polar material such assilica adsorbing a specific functional group, for performingquantitative determination using an internal standard of a non-adsorbedcomponent can be employed.

More specifically, the modification ratio is obtained by measuring anamount of adsorption onto a silica column based on a difference betweena chromatogram measured by using a polystyrene-based gel column and achromatogram measured by using a silica-based column obtained from asample solution containing a sample and low molecular weight internalstandard polystyrene. More specifically, the modification ratio ismeasured by a method described in the examples below.

In the conjugated diene-based polymer of the present embodiment, themodification ratio can be controlled by adjusting an amount of amodifier to be added and a reaction method, and thus can be controlledto be 60% by mass or more.

For example, a method in which polymerization is performed by using, asa polymerization initiator, an organic lithium compound, describedlater, having at least one nitrogen atom in a molecule, a method inwhich a monomer having at least one nitrogen atom in a molecule iscopolymerized, and a method in which a modifier having a structuralformula described later is used are combined, and polymerizationconditions are controlled, and thus, the modification ratio can beobtained.

From the viewpoints of processability and abrasion resistance balance,the conjugated diene-based polymer of the present embodiment ispreferably a conjugated diene-based polymer having a star polymerstructure having 3 or more branches, in which at least one branchedchain of the star structure comprises a portion derived from avinyl-based monomer containing an alkoxysilyl group or a halosilylgroup, and the portion derived from the vinyl-based monomer containingthe alkoxysilyl group or the halosilyl group further comprises a mainchain branch structure.

Herein, the term “star polymer structure” refers to a structure in whicha plurality of polymer chains (arms) are bonded to one central branchpoint.

The one central branch point herein contains a “substituent containingan atom derived from a coupling agent” or a “substituent containing anitrogen atom derived from a modifier”.

The term “main branch structure” herein refers to a structure in which apolymer chain forms a branch point in the portion derived from avinyl-based monomer containing an alkoxysilyl group or a halosilylgroup, and a polymer chain (arm) extends from the branch point.

In the conjugated diene-based polymer of the present embodiment, fromthe viewpoint of improving the branch number Bn, the number of mainchain branch points constituted by the portion derived from thevinyl-based monomer containing an alkoxysilyl group or a halosilyl groupis 4 or more, and a branch structure derived from a star polymerstructure formed by a modifier in a reaction step comprises preferably 3or more branches, more preferably 4 or more branches, and furtherpreferably 8 or more branches.

Although the branch number Bn is increased both by modification with acoupling agent for obtaining a star structure and by introduction of abranching agent into the polymer, contribution to the branch number Bnis larger when a whole polymer chain is branched by using a couplingagent.

In design of a polymer, the branch number Bn can be controlled inaccordance with selection of a coupling agent, and selection of a typeof and setting of an amount of a branching agent, and the branch numberBn can be more easily controlled by taking a contribution rate intoconsideration.

<Main Chain Branch Structure>

The main chain branch structure corresponds to branch points in theportion derived from the vinyl-based monomer containing an alkoxysilylgroup or a halosilyl group, and comprises 2 or more branch points,preferably 3 or more branch points, and further preferably 4 or morebranch points.

The branch point forming the main branch structure has preferably atleast 2 or more polymer chains, more preferably 3 or more polymer chainsnot corresponding to a main chain, and further preferably 4 or morepolymer chains not corresponding to a main chain.

Particularly in a main chain branch structure containing a vinyl-basedmonomer containing an alkoxysilyl group or a halosilyl group, a peakderived from the main chain branch structure is detected, in signaldetection by ²⁹Si-NMR, in a range of −45 ppm to −65 ppm, and morerestrictively in a range of −50 ppm to −60 ppm.

<Star Polymer Structure>

The conjugated diene-based polymer of the present embodiment preferablyhas a star polymer structure, and the number of branches derived fromthe star polymer structure is preferably 3 or more, more preferably 4 ormore, further preferably 6 or more, and still further preferably 8 ormore.

In a method for obtaining, as the conjugated diene-based polymer of thepresent embodiment, a conjugated diene-based polymer having a starpolymer structure comprising 3 or more branches in which at least onebranched chain of the star structure comprises a portion derived from avinyl-based monomer containing an alkoxysilyl group or a halosilylgroup, and the portion derived from the vinyl-based monomer containingthe alkoxysilyl group or the halosilyl group further comprises a mainchain branch structure, the “star polymer structure” can be formed byadjusting the number of functional groups of a modifier and an amount ofthe modifier to be added, and the “main chain branch structure” can becontrolled by adjusting the number of functional groups of a branchingagent, an amount of the branching agent to be added, and timing ofadding the branching agent.

In order to obtain a conjugated diene-based polymer having a starpolymer structure having 3 or more branches in which at least onebranched chain of the star structure comprises a portion derived from avinyl-based monomer containing an alkoxysilyl group or a halosilylgroup, and the portion derived from the vinyl-based monomer containingthe alkoxysilyl group or the halosilyl group further comprises a mainchain branch structure, for example, a method in which polymerization isperformed by using an organic lithium-based compound as a polymerizationinitiator, a branching agent for imparting a specific branch point isadded during or after the polymerization, and modification is performedby using a modifier for imparting a specific branching ratio aftercontinuation of the polymerization can be employed.

Control means for such polymerization conditions will be described lateras a production method in the examples.

(Detailed Structure of Main Chain Branch Structure) The conjugateddiene-based polymer of the present embodiment is preferably a conjugateddiene-based polymer in which the portion derived from the vinyl-basedmonomer containing an alkoxysilyl group or a halosilyl group is amonomer unit based on a compound represented by the following formula(1) or (2), comprises a branch point of a polymer chain containing themonomer unit based on the compound represented by formula (1) or (2),and has at least one end of the conjugated diene-based polymer of thepresent invention coupled by using a coupling agent, and the at leastone end of the conjugated diene-based polymer is more preferablymodified with a nitrogen atom-containing group.

In formula (1), R¹ represents a hydrogen atom, an alkyl group having 1to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, andmay have a branch structure in a part thereof.

R² and R³ each independently represent an alkyl group having 1 to 20carbon atoms, or an aryl group having 6 to 20 carbon atoms, and may havea branch structure in a part thereof. Each of R¹ to R³, if present in aplural number, is respectively independent.

X¹ represents an independent halogen atom.

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3.

In formula (2), R² to R⁵ each independently represent an alkyl grouphaving 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbonatoms, and may have a branch structure in a part thereof.

Each of R² to R⁵, if present in a plural number, is respectivelyindependent.

X² and X³ represent an independent halogen atom.

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3.

a represents an integer of 0 to 2, b represents an integer of 0 to 3, crepresents an integer of 0 to 3, and (a+b+c) is an integer of 3.

The conjugated diene-based polymer of the present embodiment preferablyhas a monomer unit based on a compound represented by formula (1) inwhich R¹ is a hydrogen atom and m is 0.

Thus, the number of branches is improved, and an effect of improvingabrasion resistance and processability can be obtained.

Alternatively, the conjugated diene-based polymer of the presentinvention is preferably a conjugated diene-based polymer having amonomer unit based on a compound represented by formula (2) in which mis 0 and b is 0.

Thus, the effect of improving abrasion resistance and processability canbe obtained.

Further alternatively, the conjugated diene-based polymer of the presentembodiment preferably has a monomer unit based on a compound representedby formula (1) in which R¹ is a hydrogen atom, m is 0 and 1 is 0.

Thus, the branch number is improved, and the effect of improvingabrasion resistance and processability is obtained.

Alternatively, the conjugated diene-based polymer of the presentembodiment is preferably a conjugated diene-based polymer having amonomer unit based on a compound represented by formula (2) in which mis 0, 1 is 0, a is 0, and b is 0.

Thus, the effect of improving abrasion resistance and processability canbe obtained.

The conjugated diene-based polymer of the present embodiment is morepreferably a conjugated diene-based polymer having a monomer unit basedon a compound represented by formula (1) in which R¹ is a hydrogen atom,1 is 0, and n is 3.

Thus, the modification ratio and the branch number are improved, and aneffect of improving low fuel consumption performance, abrasionresistance, and processability can be obtained.

[Branching Agent]

In the conjugated diene-based polymer of the present embodiment, inconstructing a main chain branch structure, a branching agentrepresented by the following formula (1) or (2) is preferably used asthe branching agent.

In formula (1), R″ represents a hydrogen atom, an alkyl group having 1to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, andmay have a branch structure in a part thereof.

R² and R³ each independently represent an alkyl group having 1 to 20carbon atoms, or an aryl group having 6 to 20 carbon atoms, and may havea branch structure in a part thereof.

Each of R″ to R³, if present in a plural number, is respectivelyindependent.

X′ represents an independent halogen atom.

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3.

In formula (2), R² to R⁵ each independently represent an alkyl grouphaving 1 to 20 carbon atoms or an aryl group having 6 to 20 carbonatoms, and may have a branch structure in a part thereof.

Each of R² to R⁵, if present in a plural number, is respectivelyindependent.

X² and X³ represent an independent halogen atom.

m represents an integer of 0 to 2, n represents an integer of 0 to 3, 1represents an integer of 0 to 3, and (m+n+1) is 3.

a represents an integer of 0 to 2, b represents an integer of 0 to 3, crepresents an integer of 0 to 3, and (a+b+c) is 3.

In the present embodiment, from the viewpoints of continuity ofpolymerization and improvement of the branch number, the branching agentused in constructing the main chain branch structure of the conjugateddiene-based polymer is preferably a compound represented by formula (1)in which R¹ is a hydrogen atom and m is 0.

Alternatively, in the present embodiment, from the viewpoint ofimprovement of the branch number, the branching agent used inconstructing the main chain branch structure of the conjugateddiene-based polymer is preferably a compound represented by formula (2)in which m is 0 and b is 0.

In the present embodiment, from the viewpoints of continuity ofpolymerization and improvement of the modification ratio and the branchnumber, the branching agent used in constructing the main chain branchstructure of the conjugated diene-based polymer is more preferably acompound represented by formula (1) in which R¹ is a hydrogen atom, m is0, and 1 is 0.

In the present embodiment, from the viewpoint of improvement of themodification ratio and the branch number, the branching agent used inconstructing the main chain branch structure of the conjugateddiene-based polymer is further preferably a compound represented byformula (2) in which m is 0, 1 is 0, a is 0, and b is 0.

In the present embodiment, from the viewpoints of continuity ofpolymerization and improvement of the modification ratio and the branchnumber, the branching agent used in constructing a main chain branchstructure of the conjugated diene-based polymer is more preferably acompound represented by formula (1) in which R¹ is a hydrogen atom, 1 is0, and n is 3.

Examples of the branching agent represented by formula (1) include, butare not limited to, trimethoxy(4-vinylphenyl)silane,triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane,tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane,trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane,tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane,triisopropoxy(3-vinylphenyl)silane, trimethoxy(2-vinylphenyl)silane,triethoxy(2-vinylphenyl)silane, tripropoxy(2-vinylphenyl)silane,tributoxy(2-vinylphenyl)silane, triisopropoxy(2-vinylphenyl)silane,dimethoxymethyl(4-vinylphenyl)silane,diethoxymethyl(4-vinylphenyl)silane,dipropoxymethyl(4-vinylphenyl)silane,dibutoxymethyl(4-vinylphenyl)silane,diisopropoxymethyl(4-vinylphenyl)silane,dimethoxymethyl(3-vinylphenyl)silane,diethoxymethyl(3-vinylphenyl)silane,dipropoxymethyl(3-vinylphenyl)silane,dibutoxymethyl(3-vinylphenyl)silane,diisopropoxymethyl(3-vinylphenyl)silane,dimethoxymethyl(2-vinylphenyl)silane,diethoxymethyl(2-vinylphenyl)silane,dipropoxymethyl(2-vinylphenyl)silane,dibutoxymethyl(2-vinylphenyl)silane,diisopropoxymethyl(2-vinylphenyl)silane,dimethylmethoxy(4-vinylphenyl)silane,dimethylethoxy(4-vinylphenyl)silane,dimethylpropoxy(4-vinylphenyl)silane,dimethylbutoxy(4-vinylphenyl)silane,dimethylisopropoxy(4-vinylphenyl)silane,dimethylmethoxy(3-vinylphenyl)silane,dimethylethoxy(3-vinylphenyl)silane,dimethylpropoxy(3-vinylphenyl)silane,dimethylbutoxy(3-vinylphenyl)silane,dimethylisopropoxy(3-vinylphenyl)silane,dimethylmethoxy(2-vinylphenyl)silane,dimethylethoxy(2-vinylphenyl)silane,dimethylpropoxy(2-vinylphenyl)silane,dimethylbutoxy(2-vinylphenyl)silane,dimethylisopropoxy(2-vinylphenyl)silane,trimethoxy(4-isopropenylphenyl)silane,triethoxy(4-isopropenylphenyl)silane,tripropoxy(4-isopropenylphenyl)silane,tributoxy(4-isopropenylphenyl)silane,triisopropoxy(4-isopropenylphenyl)silane,trimethoxy(3-isopropenylphenyl)silane,triethoxy(3-isopropenylphenyl)silane,tripropoxy(3-isopropenylphenyl)silane,tributoxy(3-isopropenylphenyl)silane,triisopropoxy(3-isopropenylphenyl)silane,trimethoxy(2-isopropenylphenyl)silane,triethoxy(2-isopropenylphenyl)silane,tripropoxy(2-isopropenylphenyl)silane,tributoxy(2-isopropenylphenyl)silane,triisopropoxy(2-isopropenylphenyl)silane,dimethoxymethyl(4-isopropenylphenyl)silane,diethoxymethyl(4-isopropenylphenyl)silane,dipropoxymethyl(4-isopropenylphenyl)silane,dibutoxymethyl(4-isopropenylphenyl)silane,diisopropoxymethyl(4-isopropenylphenyl)silane,dimethoxymethyl(3-isopropenylphenyl)silane,diethoxymethyl(3-isopropenylphenyl)silane,dipropoxymethyl(3-isopropenylphenyl)silane,dibutoxymethyl(3-isopropenylphenyl)silane,diisopropoxymethyl(3-isopropenylphenyl)silane,dimethoxymethyl(2-isopropenylphenyl)silane,diethoxymethyl(2-isopropenylphenyl)silane,dipropoxymethyl(2-isopropenylphenyl)silane,dibutoxymethyl(2-isopropenylphenyl)silane,diisopropoxymethyl(2-isopropenylphenyl)silane,dimethylmethoxy(4-isopropenylphenyl)silane,dimethylethoxy(4-isopropenylphenyl)silane,dimethylpropoxy(4-isopropenylphenyl)silane,dimethylbutoxy(4-isopropenylphenyl)silane,dimethylisopropoxy(4-isopropenylphenyl)silane,dimethylmethoxy(3-isopropenylphenyl)silane,dimethylethoxy(3-isopropenylphenyl)silane,dimethylpropoxy(3-isopropenylphenyl)silane,dimethylbutoxy(3-isopropenylphenyl)silane,dimethylisopropoxy(3-isopropenylphenyl)silane,dimethylmethoxy(2-isopropenylphenyl)silane,dimethylethoxy(2-isopropenylphenyl)silane,dimethylpropoxy(2-isopropenylphenyl)silane,dimethylbutoxy(2-isopropenylphenyl)silane,dimethylisopropoxy(2-isopropenylphenyl)silane,trichloro(4-vinylphenyl)silane, trichloro(3-vinylphenyl)silane,trichloro(2-vinylphenyl)silane, tribromo(4-vinylphenyl)silane,tribromo(3-vinylphenyl)silane, tribromo(2-vinylphenyl)silane,dichloromethyl(4-vinylphenyl)silane,dichloromethyl(3-vinylphenyl)silane,dichloromethyl(2-vinylphenyl)silane, dibromomethyl(4-vinylphenyl)silane,dibromomethyl(3-vinylphenyl)silane, dibromomethyl(2-vinylphenyl)silane,dimethylchloro(4-vinylphenyl)silane,dimethylchloro(3-vinylphenyl)silane,dimethylchloro(2-vinylphenyl)silane, dimethylbromo(4-vinylphenyl)silane,dimethylbromo(3-vinylphenyl)silane, anddimethylbromo(2-vinylphenyl)silane.

Among these, trimethoxy(4-vinylphenyl)silane,triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane,tributoxy(4-vinylphenyl)silane, triisopropoxy(4-vinylphenyl)silane,trimethoxy(3-vinylphenyl)silane, triethoxy(3-vinylphenyl)silane,tripropoxy(3-vinylphenyl)silane, tributoxy(3-vinylphenyl)silane,triisopropoxy(3-vinylphenyl)silane, and trichloro(4-vinylphenyl)silaneare preferred, and trimethoxy(4-vinylphenyl)silane,triethoxy(4-vinylphenyl)silane, tripropoxy(4-vinylphenyl)silane,tributoxy(4-vinylphenyl)silane, and triisopropoxy(4-vinylphenyl)silaneare more preferred.

Examples of the branching agent represented by formula (2) include, butare not limited to, 1,1-bis(4-trimethoxysilylphenyl)ethylene,1,1-bis(4-triethoxysilylphenyl)ethylene,1,1-bis(4-tripropoxysilylphenyl)ethylene,1,1-bis(4-tripentoxysilylphenyl)ethylene,1,1-bis(4-triisopropoxysilylphenyl)ethylene,1,1-bis(3-trimethoxysilylphenyl)ethylene,1,1-bis(3-triethoxysilylphenyl)ethylene,1,1-bis(3-tripropoxysilylphenyl)ethylene,1,1-bis(3-tripentoxysilylphenyl)ethylene,1,1-bis(3-triisopropoxysilylphenyl)ethylene,1,1-bis(2-trimethoxysilylphenyl)ethylene,1,1-bis(2-triethoxysilylphenyl)ethylene,1,1-bis(3-tripropoxysilylphenyl)ethylene,1,1-bis(2-tripentoxysilylphenyl)ethylene,1,1-bis(2-triisopropoxysilylphenyl)ethylene,1,1-bis(4-(dimethylmethoxysilyl)phenyl)ethylene,1,1-bis(4-(diethylmethoxysilyl)phenyl)ethylene,1,1-bis(4-(dipropylmethoxysilyl)phenyl)ethylene,1,1-bis(4-(dimethylethoxysilyl)phenyl)ethylene,1,1-bis(4-(diethylethoxysilyl)phenyl)ethylene, and1,1-bis(4-(dipropylethoxysilyl)phenyl)ethylene.

Among these, 1,1-bis(4-trimethoxysilylphenyl)ethylene,1,1-bis(4-triethoxysilylphenyl)ethylene,1,1-bis(4-tripropoxysilylphenyl)ethylene,1,1-bis(4-tripentoxysilylphenyl)ethylene, and1,1-bis(4-triisopropoxysilylphenyl)ethylene are preferred, and1,1-bis(4-trimethoxysilylphenyl)ethylene is more preferred.

[Production Method for Conjugated Diene-Based Polymer]

A production method for a conjugated diene-based polymer of the presentembodiment comprises a polymerizing/branching step of polymerizing atleast a conjugated diene compound in the presence of an organiclithium-based compound to obtain a conjugated diene-based polymer havinga main chain branch structure by using at least any one of the variousbranching agents described above; and a step of coupling the conjugateddiene-based polymer by using a coupling agent and/or a step of modifyingthe conjugated diene-based polymer with a modifier having a nitrogenatom-containing group.

The conjugated diene-based polymer contained in a modified conjugateddiene-based polymer may be any one of a homopolymer of a singleconjugated diene compound, a polymer, namely, a copolymer, of differentkinds of conjugated diene compounds, and a copolymer of a conjugateddiene compound and an aromatic vinyl compound.

(Polymerizing/Branching Step)

In the polymerizing/branching step in the production method for theconjugated diene-based polymer of the present embodiment, an organiclithium-based compound, such as an organomonolithium compound, is usedas a polymerization initiator to polymerize at least a conjugated dienecompound, and a branching agent is added thereto to obtain a conjugateddiene-based polymer having a main chain branch structure.

In the polymerizing step, the polymerization is performed preferably bya growth reaction by a living anionic polymerization reaction, and thus,a conjugated diene-based polymer having an active end can be obtained.Thereafter, also in the branching step using a branching agent, mainchain branching can be appropriately controlled, and there is a tendencythat a modified conjugated diene-based polymer having a highmodification ratio can be obtained by continuing the polymerization onthe active end after the main chain branching.

<Polymerization Initiator>

As a polymerization initiator, an organic lithium-based compound isused, and at least an organomonolithium compound is preferably used.

An example of the organomonolithium compound includes, but is notlimited to, an organomonolithium compound of a low molecular weightcompound or a soluble oligomer.

Examples of the organomonolithium compound include, with respect to abonding mode between an organic group and lithium thereof, a compoundhaving a carbon-lithium bond, a compound having a nitrogen-lithium bond,and a compound having a tin-lithium bond.

An amount of the organomonolithium compound to be used as thepolymerization initiator is preferably determined on the basis of themolecular weight of a target conjugated diene-based polymer.

A ratio of the amount of a monomer such as a conjugated diene compoundto be used to the amount of the polymerization initiator to be usedrelates to the degree of polymerization of the target conjugateddiene-based polymer. In other words, there is a tendency that it relatesto the number average molecular weight and/or the weight averagemolecular weight.

Accordingly, in order to increase the molecular weight of the conjugateddiene-based polymer, adjustment may be made to reduce the amount of thepolymerization initiator, and in order to reduce the molecular weight,the adjustment may be made to increase the amount of the polymerizationinitiator.

From the viewpoint that it is used as one method for introducing anitrogen atom into a conjugated diene-based polymer, theorganomonolithium compound is preferably an alkyl lithium compoundhaving a substituted amino group or dialkylamino lithium.

In this case, a conjugated diene-based polymer having, at apolymerization starting end, a nitrogen atom of an amino group isobtained.

The substituted amino group refers to an amino group having no activehydrogen or having a structure in which active hydrogen is protected.

Examples of an alkyl lithium compound containing an amino group havingno active hydrogen include, but are not limited to,3-dimethylaminopropyl lithium, 3-diethylaminopropyl lithium,4-(methylpropylamino)butyl lithium and 4-hexamethyleneiminobutyllithium.

Examples of an alkyl lithium compound containing an amino group having astructure in which active hydrogen is protected include, but are notlimited to, 3-bistrimethylsilylaminopropyl lithium and4-trimethylsilylmethylaminobutyl lithium.

Examples of the dialkylamino lithium include, but are not limited to,lithium dimethylamide, lithium diethylamide, lithium dipropylamide,lithium dibutylamide, lithium di-n-hexylamide, lithium diheptylamide,lithium diisopropylamide, lithium dioctylamide,lithium-di-2-ethylhexylamide, lithium didecylamide, lithiumethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide,lithium methylphenetylamide, lithium hexamethyleneimide, lithiumpyrrolidide, lithium piperidide, lithium heptamethyleneimide, lithiummorpholide, 1-lithioazacyclooctane,6-lithio-1,3,3-trimethyl-6-azabicyclo[3.2.1] octane, and1-lithio-1,2,3,6-tetrahydropyridine.

Such an organomonolithium compound having a substituted amino group canbe reacted with a small amount of a polymerizable monomer, such as1,3-butadiene, isoprene or styrene, to be used as an organomonolithiumcompound of an oligomer soluble in normal hexane or cyclohexane.

From the viewpoint of the industrial availability and thecontrollability of the polymerization reaction, the organomonolithiumcompound is preferably an alkyl lithium compound. In this case, aconjugated diene-based polymer having an alkyl group at a polymerizationstarting end can be obtained.

Examples of the alkyl lithium compound include, but are not limited to,n-butyllithium, sec-butyllithium, tert-butyllithium, n-hexyllithium,benzyllithium, phenyllithium, and stilbene lithium.

From the viewpoint of the industrial availability and thecontrollability of the polymerization reaction, the alkyl lithiumcompound is preferably n-butyllithium or sec-butyllithium.

One of these organomonolithium compounds may be singly used, or two ormore of these may be used together. Alternatively, another organic metalcompound may be used together.

Examples of such another organic metal compound include alkaline earthmetal compounds, other alkaline metal compounds, and other organic metalcompounds.

Examples of the alkaline earth metal compounds include, but are notlimited to, organic magnesium compounds, organic calcium compounds andorganic strontium compounds. Other examples include compounds ofalkoxides, sulfonates, carbonates and amides of alkaline earth metals.

Examples of the organic magnesium compounds include dibutyl magnesiumand ethyl butyl magnesium. Examples of the other organic metal compoundsinclude organic aluminum compounds.

Examples of a polymerization reaction mode employed in the polymerizingstep include, but are not limited to, batch and continuouspolymerization reaction modes.

In the continuous mode, one reactor or two or more connected reactorscan be used. As a reactor for the continuous mode, for example, a tankor tubular reactor equipped with a stirrer can be used. In thecontinuous mode, a monomer, an inert solvent and a polymerizationinitiator are continuously fed to the reactor, a polymer solutioncontaining a polymer is obtained in the reactor, and the polymersolution is continuously discharged.

As a reactor for the batch mode, for example, a tank reactor equippedwith a stirrer is used. It is preferable, in the batch mode, that amonomer, an inert solvent and a polymerization initiator are fed to thereactor, the monomer is continuously or intermittently additionally fedif necessary during the polymerization, a polymer solution containing apolymer is obtained in the reactor, and the polymer solution isdischarged after completing the polymerization.

In the production method for the conjugated diene-based polymer of thepresent embodiment, in order to obtain a conjugated diene-based polymerhaving an active end at a high ratio, the continuous mode in which apolymer is continuously discharged to be supplied to a next reaction ina short period of time is preferably employed.

In the polymerizing step for a conjugated diene-based polymer, thepolymerization is performed preferably in an inert solvent.

Examples of the inert solvent include hydrocarbon-based solvents such assaturated hydrocarbons and aromatic hydrocarbons. Specific examples ofthe hydrocarbon-based solvent include, but are not limited to, aliphatichydrocarbons such as butane, pentane, hexane and heptane; alicyclichydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane andmethylcyclohexane; aromatic hydrocarbons such as benzene, toluene andxylene; and a hydrocarbon containing a mixture of any of these.

Impurities of allenes and acetylenes are preferably treated with anorganic metal compound before the solvent is supplied to thepolymerization reaction because thus, a conjugated diene-based polymerhaving an active end in a high concentration tends to be obtained, and amodified conjugated diene-based polymer having a high modification ratiotends to be obtained.

In the polymerizing step, a polar compound may be added. Thus, anaromatic vinyl compound can be randomly copolymerized with a conjugateddiene compound, and there is a tendency that the polar compound can beused also as a vinylation agent for controlling a microstructure of aconjugated diene portion. Besides, it tends to be advantageous for, forexample, acceleration of the polymerization reaction.

Examples of the polar compound include, but are not limited to, etherssuch as tetrahydrofuran, diethyl ether, dioxane, ethylene glycoldimethyl ether, ethylene glycol dibutyl ether, diethylene glycoldimethyl ether, diethylene glycol dibutyl ether, dimethoxybenzene, and2,2-bis(2-oxolanyl)propane; tertiary amine compounds such astetramethylethylenediamine, dipiperidinoethane, trimethylamine,triethylamine, pyridine, and quinuclidine; alkaline metal alkoxidecompounds such as potassium-tert-amylate, potassium-tert-butylate,sodium-tert-butylate, and sodium amylate; and phosphine compounds suchas triphenylphosphine.

One of these polar compounds may be singly used, or two or more of thesemay be used together.

The amount of the polar compound to be used is not especially limitedbut can be selected in accordance with the purpose or the like, and ispreferably 0.01 mol or more and 100 mol or less per mole of thepolymerization initiator.

Such a polar compound (a vinylation agent) can be used, as amicrostructure modifier for a conjugated diene portion of the conjugateddiene-based polymer, in an appropriate amount in accordance with adesired amount of bound vinyl.

There is a tendency that many polar compounds simultaneously have aneffective randomizing effect in copolymerization of a conjugated dienecompound and an aromatic vinyl compound, and can be used as a modifierfor the distribution of the aromatic vinyl compound and the amount of astyrene block.

As a method for randomizing the conjugated diene compound and thearomatic vinyl compound, for example, a method as described in JapanesePatent Laid-Open No. 59-140211 in which a copolymerization reaction isstarted with the whole amount of styrene and a part of 1,3-butadienewith the rest of 1,3-butadiene intermittently added during thecopolymerization reaction may be employed.

In the polymerizing step, a polymerization temperature is preferably atemperature at which the living anionic polymerization proceeds, andfrom the viewpoint of productivity, is more preferably 0° C. or more,and more preferably 120° C. or less. If the polymerization temperaturefalls in this range, there is a tendency that a reaction amount of themodifier reacted to the active end can be sufficiently attained aftercompleting the polymerization. The polymerization temperature is furtherpreferably 50° C. or more and 100° C. or less.

In the production method for the conjugated diene-based polymer of thepresent embodiment, the amount of the branching agent to be added in thebranching step for forming a main chain branch structure is notespecially limited but can be selected in accordance with the purpose orthe like, and is preferably 0.03 mol or more and 0.5 mol or less, morepreferably 0.05 mol or more and 0.4 mol or less, and further preferably0.01 mol or more and 0.25 mol or less per mole of the polymerizationinitiator.

The branching agent can be used in an appropriate amount in accordancewith the number of branch points of a main chain branch structure of theconjugated diene portion of the target conjugated diene-based polymer.

The timing of adding the branching agent in the branching step is notespecially limited but can be selected in accordance with the purpose orthe like, and from the viewpoints of the improvement of the absolutemolecular weight of the conjugated diene-based polymer and theimprovement of the modification ratio, is timing, after adding thepolymerization initiator, when a raw material conversion rate ispreferably 20% or more, more preferably 40% or more, further preferably50% or more, still further preferably 65% or more, and much furtherpreferably 75% or more.

After the addition of the branching agent, a desired raw material may beadditionally added to continue the polymerizing step after thebranching, or the above-described process may be repeated.

An amount of a monomer to be additionally added is not especiallylimited, and from the viewpoint of the improvement of the modificationratio of the conjugated diene-based polymer, is preferably 5% or more,more preferably 10% or more, further preferably 15% or more, stillfurther preferably 20% or more, and much further preferably 25% or morebased on the total amount of conjugated diene-based monomers, forexample, the total amount of butadiene, used in the polymerizing step.

The conjugated diene-based polymer obtained, prior to the modificationreaction step, by the polymerizing/branching step in the productionmethod for the conjugated diene-based polymer of the present embodimenthas a Mooney viscosity, measured at 110° C., of preferably 10 or moreand 150 or less, more preferably 15 or more and 140 or less, and furtherpreferably 20 or more and 130 or less.

If the Mooney viscosity falls in this range, the conjugated diene-basedpolymer of the present embodiment tends to be excellent inprocessability and abrasion resistance.

The conjugated diene-based polymer of the present embodiment may be apolymer of a conjugated diene monomer and a branching agent, or may be acopolymer of a conjugated diene monomer, a branching agent, and anothermonomer.

For example, when the conjugated diene monomer is butadiene or isoprene,and this diene monomer is polymerized with a branching agent containingan aromatic vinyl portion, a polymer chain is what is calledpolybutadiene or polyisoprene, and a polymer containing a structurederived from an aromatic vinyl in a branched portion is obtained. Owingto such a structure, linearity of each polymer chain can be improved anda crosslink density obtained after vulcanization can be improved,resulting in obtaining an effect of improving the abrasion resistance ofthe polymer. Therefore, such a polymer is suitably used for a tire,resin modification, interior/exterior of a vehicle, an anti-vibrationrubber, shoes and the like.

When the conjugated diene-based polymer is used in application to a tiretread, a copolymer of a conjugated diene monomer, an aromatic vinylmonomer, and a branching agent is suitably used, and in the copolymerused in this application, the amount of bound conjugated diene ispreferably 40% by mass or more and 100% by mass or less, and morepreferably 55% by mass or more and 80% by mass or less.

Besides, the amount of bound aromatic vinyl in the conjugateddiene-based polymer of the present embodiment is not especially limited,and is preferably 0% by mass or more and 60% by mass or less, and morepreferably 20% by mass or more and 45% by mass or less.

When the amounts of the bound conjugated diene and the bound aromaticvinyl fall in the above-described ranges, the balance between a lowhysteresis loss property and wet skid resistance, abrasion resistanceand fracture performance obtained when in the form of a vulcanizate tendto be more excellent.

Here, the amount of bound aromatic vinyl can be measured in accordancewith UV absorption by a phenyl group, and based on the thus obtainedamount, the amount of bound conjugated diene can be also obtained.Specifically, these amounts are measured in accordance with a methoddescribed later in the examples.

In the conjugated diene-based polymer of the present embodiment, theamount of bound vinyl in a conjugated diene bond unit is not especiallylimited, and is preferably 10% by mol or more and 75% by mol or less,and more preferably 20% by mol or more and 65% by mol or less.

If the amount of bound vinyl falls in the above-described range, thebalance between a low hysteresis loss property and wet skid resistance,abrasion resistance, and fracture strength obtained when in the form ofa vulcanizate tend to be more excellent.

Here, if the modified diene-based polymer is a copolymer of butadieneand styrene, the amount of bound vinyl (the amount of a 1,2-bond) in abutadiene bond unit can be obtained by Hampton method (R. R. Hampton,Analytical Chemistry, 21, 923 (1949)). Specifically, it can be measuredby a method described in the examples below.

As for the microstructure of the conjugated diene-based polymer, if theamounts of the aforementioned bonds in the conjugated diene-basedpolymer of the present embodiment respectively fall in theabove-described ranges and the glass transition temperature of theconjugated diene-based polymer is −70° C. or more and −15° C. or less,there is a tendency that a vulcanizate more excellent in the balancebetween a low hysteresis loss property and wet skid resistance can beobtained.

The glass transition temperature is defined as a peak top (an inflectionpoint) of a DSC differential curve obtained by recording a DSC curveduring temperature increase in a prescribed temperature range inaccordance with ISO 22768:2006. Specifically, it can be measured inaccordance with a method described in the examples below.

If the conjugated diene-based polymer of the present embodiment is aconjugated diene-aromatic vinyl copolymer, it preferably contains a fewor no blocks in which 30 or more aromatic vinyl units are chained. Morespecifically, if the conjugated diene-based polymer of the presentembodiment is a butadiene-styrene copolymer, in employing a known methodin which the copolymer is decomposed by Kolthoff method (a methoddescribed by I. M. Kolthoff, et al., J. Polym. Sci. 1, 429 (1946)) toanalyze the amount of polystyrene insoluble in methanol, blocks in eachof which 30 or more aromatic vinyl units are chained are preferably 5.0%by mass or less, and more preferably 3.0% by mass or less based on thetotal amount of the conjugated diene-based polymer.

From the viewpoint of improving fuel efficiency, if the conjugateddiene-based polymer of the present embodiment is a conjugateddiene-aromatic vinyl copolymer, a larger proportion of an aromatic vinylunit is preferably present singly.

Specifically, if the conjugated diene-based polymer of the presentembodiment is a butadiene-styrene copolymer, when the conjugateddiene-based polymer is decomposed by employing a method throughozonolysis known as a method of Tanaka et al., (Polymer, 22, 1721(1981)) to analyze a styrene chain distribution by GPC, it is preferablethat the amount of isolated styrene, based on the whole amount of boundstyrene, is 40% by mass or more, and that the amount of a chain styrenestructure consisting of 8 or more chained styrene is 5.0% by mass orless.

In this case, a resultant vulcanized rubber tends to attain excellentperformance of particularly low hysteresis loss.

(Reaction Step)

In the production method for the conjugated diene-based polymer of thepresent embodiment, a step of coupling an active end of the conjugateddiene-based polymer obtained through the polymerizing/branching stepwith a coupling agent, such as a tri- or higher functional reactivecompound and/or a step of modifying it with a modifier containing anitrogen atom-containing group (preferably a coupling agent containing anitrogen atom-containing group) are performed.

Hereinafter, the step of coupling and/or the step of modifying theactive end will be referred to as a reaction step.

In the reaction step, one end of the active end of the conjugateddiene-based polymer is subjected to a modification reaction with acoupling agent or a nitrogen atom-containing group, and thus, a modifiedconjugated diene-based polymer is obtained.

<Coupling Agent>

The coupling agent used in the reaction step of the production methodfor the conjugated diene-based polymer of the present embodiment mayhave any structure as long as it is a tri- or higher functional reactivecompound, and is preferably a tri- or higher functional reactivecompound having a silicon atom, and more preferably one having at least4 silicon-containing functional groups. A more preferable coupling agentis a compound in which at least one silicon atom constitutes analkoxysilyl group or silanol group having 1 to 20 carbon atoms. Examplesof such a coupling agent include tetramethoxysilane andtetraethoxysilane.

<Modifier>

Examples of the modifier include, but are not limited to,tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine,tris(3-tripropoxysilylpropyl)amine,bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine,tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine,tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-methyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane,tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,tetrakis(3-trimethoxysilylpropyl)-1,6-hexamethylenediamine,pentakis(3-trimethoxysilylpropyl)-diethylenetriamine,tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine,tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-1-trimethylsilyl-1-sila-2-azacyclopentane)propyl]silane,3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-trimethoxysilylpropane,1-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexane,1-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexane,3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexyl-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]ether, (3-trimethoxysilylpropyl) phosphate,bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]phosphate,bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)phosphate, and tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]phosphate.

The modifier preferably contains a compound represented by any one ofthe following general formulas (A) to (C):

wherein R¹ to R⁴ each independently represent an alkyl group having 1 to20 carbon atoms or an aryl group having 6 to 20 carbon atoms, R⁵represents an alkylene group having 1 to 10 carbon atoms, R⁶ representsan alkylene group having 1 to 20 carbon atoms, m represents an integerof 1 or 2, n represents an integer of 2 or 3, (m+n) is an integer of 4or more, and each of R¹ to R⁴, if present in a plural number, isrespectively independent.

wherein R¹ to R⁶ each independently represent an alkyl group having 1 to20 carbon atoms or an aryl group having 6 to 20 carbon atoms, R⁷ to R⁹each independently represent an alkylene group having 1 to 20 carbonatoms, m, n, and 1 each independently represent an integer of 1 to 3,(m+n+1) is an integer of 4 or more, and each of R¹ to R⁶, if present ina plural number, is respectively independent.

wherein R¹² to R¹⁴ each independently represent a single bond or analkylene group having 1 to 20 carbon atoms, R¹⁵ to R¹⁹ and R²⁰ eachindependently represent an alkyl group having 1 to 20 carbon atoms, R¹⁹and R²² each independently represent an alkylene group having 1 to 20carbon atoms, R²¹ represents an alkyl group or a trialkyl silyl grouphaving 1 to 20 carbon atoms, m represents an integer of 1 to 3, prepresents 1 or 2, each of R¹² to R²², m and p, if present in a pluralnumber, is respectively independent, and may be the same or different, irepresents an integer of 0 to 6, j represents an integer of 0 to 6, krepresents an integer of 0 to 6, (i+j+k) is an integer of 4 to 10, and Arepresents a hydrocarbon group having 1 to 20 carbon atoms, or anorganic group having at least one atom selected from the groupconsisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfuratom, and a phosphorus atom, and not having active hydrogen.

Examples of the modifier represented by formula (A) include, but are notlimited to,2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane,2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane,2,2-dimethoxy-1-(4-trimethoxysilylbutyl)-1-aza-2-silacyclohexane,2,2-dimethoxy-1-(5-trimethoxysilylpentyl)-1-aza-2-silacycloheptane,2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane,2,2-diethoxy-1-(3-diethoxyethylsilylpropyl)-1-aza-2-silacyclopentane,2-methoxy-2-methyl-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane,2-ethoxy-2-ethyl-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane,2-methoxy-1-methyl-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane,and2-ethoxy-2-ethyl-1-(3-diethoxyethylsilylpropyl)-1-aza-2-silacyclopentane.

Among these, from the viewpoint of reactivity and interactivity betweena functional group of the modifier and an inorganic filler such assilica, and from the viewpoint of processability, it is preferable thatm is 2 and that n is 3. Specifically,2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane and2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane arepreferred.

The reaction temperature, the reaction time and the like in causing themodifier represented by formula (A) to react with the polymer active endare not especially limited, and it is preferable to perform the reactionat 0° C. or more and 120° C. or less for 30 seconds or more.

A total mole number of an alkoxy group bonded to a silyl group of thecompound used as the modifier represented by formula (A) is preferably0.6 or more times and 3.0 or less times, more preferably 0.8 or moretimes and 2.5 or less times, and further preferably 0.8 or more timesand 2.0 or less times of a mole number of an alkaline metal compoundand/or an alkaline earth metal compound of a polymerization initiator tobe added. From the viewpoint that the thus obtained modified conjugateddiene-based polymer has sufficient modification ratio and molecularweight and has a branch structure, the total mole number is preferably0.6 times or more, and a branched polymer component is preferablyobtained by coupling polymer ends for improving processability, and inaddition, from the viewpoint of cost of a modifier, the total molenumber is preferably 3.0 times or less.

More specific mole number of the polymerization initiator is preferably3.0-fold moles or more, and more preferably 4.0-fold moles or morerelative to the mole number of the modifier.

Examples of the modifier represented by formula (B) include, but are notlimited to, tris(3-trimethoxysilylpropyl) amine,tris(3-methyldimethoxysilylpropyl)amine,tris(3-triethoxysilylpropyl)amine,tris(3-methyldiethoxysilylpropyl)amine,tris(trimethoxysilylmethyl)amine, tris(2-trimethoxysilylethyl)amine, andtris(4-trimethoxysilylbutyl)amine.

Among these, from the viewpoint of reactivity and interactivity betweena functional group of the modifier and an inorganic filler such assilica, and from the viewpoint of processability, it is preferable thatn, m and 1 are all 3. Specific preferable examples includetris(3-trimethoxysilylpropyl)amine, andtris(3-triethoxysilylpropyl)amine.

The reaction temperature, the reaction time and the like in causing themodifier represented by formula (B) to react with the polymer active endare not especially limited, and it is preferable to perform the reactionat 0° C. or more and 120° C. or less for 30 seconds or more.

A total mole number of an alkoxy group bonded to a silyl group of thecompound used as the modifier represented by formula (B) is preferably0.6 or more times and 3.0 or less times, more preferably 0.8 or moretimes and 2.5 or less times, and further preferably 0.8 or more timesand 2.0 or less times of a mole number of lithium contained in apolymerization initiator to be added. From the viewpoint that themodified conjugated diene-based polymer has sufficient modificationratio and molecular weight and has a branch structure, the total molenumber is preferably 0.6 times or more, and a branched polymer componentis preferably obtained by coupling polymer ends for improvingprocessability, and in addition, from the viewpoint of cost of amodifier, the total mole number is preferably 3.0 times or less.

More specific mole number of the polymerization initiator is preferably4.0-fold moles or more, and more preferably 5.0-fold moles or morerelative to the mole number of the modifier.

In formula (C), A is preferably represented by any one of the followinggeneral formulas (II) to (V):

wherein B¹ represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, a represents an integer of 1 to 10, and B¹, if presentin a plural number, is respectively independent;

wherein B² represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, B³ represents an alkyl group having 1 to 20 carbonatoms, a represents an integer of 1 to 10, and each of B² and B³, ifpresent in a plural number, is respectively independent;

wherein B⁴ represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, a represents an integer of 1 to 10, and B⁴, if presentin a plural number, is respectively independent; and

wherein B⁵ represents a single bond or a hydrocarbon group having 1 to20 carbon atoms, a represents an integer of 1 to 10, and B⁵, if presentin a plural number, is respectively independent.

Examples of the modifier represented by formula (C) wherein A isrepresented by formula (II) include, but are not limited to,tris(3-trimethoxysilylpropyl)amine,bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine,bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)amine,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine,tris(3-ethoxysilylpropyl)amine,bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacylopentane)propyl]amine,bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)amine,tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]amine,tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine,tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanedimane,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)1,3-propanediamine,tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-azacyclopentane)propyl]-1,3-propanediamine,bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,tetrakis(3-triethoxysilylpropyl)-1,3-propanediamine,tris(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,bis(3-triethoxysilylpropyl)-bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-1,3-propanediamine,tetrakis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tris(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine,tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane,tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethycyclohexane,bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane,tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-biasminomethylcyclohexane,tris[3-(2,2-dimethoxy-1-aza-2-cyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,tetrakis(3-triethoxysilylpropyl)-1,3-propanediamine,tris(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,bis(3-trimethoxysilylpropyl)-bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-1,3-propanediamine,tetrakis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tris(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane,tetrakis(3-trimethoxysilylpropyl)-1,6-hexamethylenediamine andpentakis(3-trimethoxysilylpropyl)-diethylenetriamine

Examples of the modifier represented by formula (C) wherein A isrepresented by formula (III) include, but are not limited to,tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine,bis(2-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine,bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine,tris(3-triethoxysilylpropyl)-methyl-1,3-propanediamine,bis(2-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine,bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-methyl-1,3-propanediamine,N¹,N¹′-(propane-1,3-diyl)bis(N¹-methyl-N³,N³-bis(3-(trimethoxysilyl)propyl)-1,3-propanediamine)andN¹-(3-(bis(3-(trimethoxysilyl)propyl)amino)propyl)-N¹-methyl-N³-(3-(methyl(3-(trimethoxysilyl)propyl)amino)propyl)-N³-(3-(trimethoxysilyl)propyl)-1,3-propanediamine

Examples of the modifier represented by formula (C) wherein A isrepresented by formula (IV) include, but are not limited to,tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane,tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]silane,bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,(3-trimethoxysilyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,bis[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,bis(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane,bis[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-bis(3-trimethoxysilylpropyl)silane,andbis(3-trimethoxysilylpropyl)-bis[3-(1-methoxy-2-methyl-1-sila-2-azacyclopentane)propyl]silane.

Examples of the modifier represented by formula (C) wherein A isrepresented by formula (V) include, but are not limited to,3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-(2,2-dimethoxy-1-aza-2-silacyclopentane)propane,and3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-trimethoxysilylpropane.

In formula (C), A is preferably represented by formula (II) or formula(III), and k represents 0 (zero).

Such a modifier tends to be easily available, and tends to make theresultant conjugated diene-based polymer of the present embodiment moreexcellent in abrasion resistance and a low hysteresis loss property whenin the form of a vulcanizate.

Examples of such a modifier include, but are not limited to,bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine,tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine,tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine,tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane,tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, andbis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine.

In formula (C), it is more preferable that A is represented by formula(II) or formula (III), and that k represents 0 (zero) and a representsan integer of 2 to 10 in formula (II) or formula (III).

Thus, abrasion resistance and a low hysteresis loss property when in theform of a vulcanizate tend to be more excellent.

Examples of such a modifier include, but are not limited to,tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine,tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine,tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, andN¹-(3-(bis(3-(trimethoxysilyl)propyl)amino)propyl)-N¹-methyl-N³-(3-(methyl(3-(trimethoxysilyl)propyl)amino)propyl)-N³-(3-(trimethoxysilyl)propyl)-1,3-propanediamine.

The amount of the compound represented by formula (C) to be added as themodifier can be adjusted for causing the modifier to react with theconjugated diene-based polymer in such a manner that a mole number ofthe modifier relative to a mole number of the conjugated diene-basedpolymer can be in a desired stoichiometric ratio, and thus, a desiredstar polymer branch structure tends to be attained.

Specifically, the mole number of the conjugated diene-based polymer ispreferably 5.0-fold moles or more, and more preferably 6.0-fold moles ormore relative to the mole number of the modifier.

In this case, in formula (C), the number of functional groups((m−1)×i+p×j+k) of the modifier is preferably an integer of 5 to 10, andmore preferably an integer of 6 to 10.

In the modified conjugated diene-based polymer of the presentembodiment, a ratio of a modifying group-containing polymer in theconjugated diene-based polymer is expressed as a modification ratio.

In the conjugated diene-based polymer of the present embodiment, themodification ratio is preferably 60% by mass or more, more preferably65% by mass or more, further preferably 70% by mass or more, stillfurther preferably 75% by mass or more, much further preferably 80% bymass or more, and particularly preferably 82% by mass or more.

If the modification ratio is 60% by mass or more, there is a tendencythat processability obtained when used for obtaining a vulcanizate isexcellent, and abrasion resistance and a low hysteresis loss propertywhen in the form of a vulcanizate are more excellent.

In the present embodiment, a condensation reaction step of performing acondensation reaction in the presence of a condensation accelerator maybe performed after the reaction step, or before the reaction step.

The conjugated diene-based polymer of the present embodiment may behydrogenated in the conjugated diene portion thereof.

A method for hydrogenating the conjugated diene portion of the modifiedconjugated diene-based polymer of the present embodiment is notespecially limited, and any of known methods can be employed.

As a suitable hydrogenation method, a method in which the hydrogenationis performed by blowing gaseous hydrogen into the polymer solution inthe presence of a catalyst can be employed.

Examples of the catalyst include heterogeneous catalysts such as acatalyst containing a noble metal supported on a porous inorganicsubstance; and homogenous catalysts such as a catalyst obtained byreacting a solubilized salt of nickel, cobalt or the like with organicaluminum or the like, and a catalyst using metallocene such astitanocene. Among these catalysts, from the viewpoint that a mildhydrogenation condition can be selected, a titanocene catalyst ispreferably used.

In addition, hydrogenation of an aromatic group can be performed byusing a noble metal-supported catalyst.

Examples of the hydrogenation catalyst include, but are not limited to,(1) a supported heterogeneous hydrogenation catalyst obtained bysupporting a metal such as Ni, Pt, Pd or Ru on carbon, silica, aluminaor diatomite, (2) what is called a ziegler catalyst using an organicacid salt of Ni, Co, Fe, Cr or the like, or a transition metal salt suchas acetylacetone salt, and a reducing agent such as organic aluminum,and (3) what is called an organic metal complex such as an organic metalcompound of Ti, Ru, Rh or Zr. Furthermore, examples of the hydrogenationcatalyst include known hydrogenation catalysts described in, forexample, Japanese Patent Publication No. 42-8704, Japanese PatentPublication No. 43-6636, Japanese Patent Publication No. 63-4841,Japanese Patent Publication No. 1-37970, Japanese Patent Publication No.1-53851, Japanese Patent Publication No. 2-9041 and Japanese PatentLaid-Open No. 8-109219. A preferable hydrogenation catalyst is areaction mixture of a titanocene compound and a reducing organic metalcompound.

In the method for producing the conjugated diene-based polymer of thepresent embodiment, a deactivator, a neutralizer or the like may beadded if necessary to the resultant polymer solution after the reactionstep.

Examples of the deactivator include, but are not limited to, water; andalcohols such as methanol, ethanol and isopropanol.

Examples of the neutralizer include, but are not limited to, carboxylicacids such as stearic acid, oleic acid and versatic acid (a mixture ofhighly branched carboxylic acids having 9 to 11 carbon atoms, mainly 10carbon atoms); and an aqueous solution of an inorganic acid, and acarbon dioxide gas.

To the conjugated diene-based polymer of the present embodiment, fromthe viewpoint of preventing gel formation after the polymerization andof improving stability in the processing, a stabilizer for rubber ispreferably added.

As the stabilizer for rubber, any of known stabilizers, not limited tothe following, can be used, and preferable examples include antioxidantssuch as 2,6-di-tert-butyl-4-hydroxytoluene (BHT),n-octadecyl-3-(4′-hydroxy-3′,5′-di-tert-butylphenol)propionate, and2-methyl-4,6-bis[(octylthio)methyl]phenol.

(Extended Conjugated Diene-Based Polymer)

An extended conjugated diene-based polymer of the present embodimentcontains the conjugated diene-based polymer of the present embodimentdescribed above, and at least any one selected from the group consistingof an extender oil, a liquid rubber, and a resin.

It is noted that the extended conjugated diene-based polymer encompassesnot only an extended conjugated diene-based polymer containing an oilbut also one containing a liquid polybutadiene excluding an oil, or anyof various resins.

Thus, the processability of the conjugated diene-based polymer can befurther improved.

A preferable example of a method for adding an extender oil to theconjugated diene-based polymer includes, but is not limited to, a methodin which an extender oil is added to a conjugated diene-based polymersolution to be mixed, and the resultant extended polymer solution isdesolvated.

Examples of the extender oil include an aroma oil, a naphthenic oil anda paraffin oil. Among these oils, from the viewpoint of environmentalsafety, oil bleeding prevention and wet grip characteristics, anaroma-alternative oil containing 3% by mass or less of a polycyclicaromatic (PCA) component according to the IP 346 is preferred. Examplesof the aroma-alternative oil include TDAE (Threated Distillate AromaticExtracts), MES (Mild Extraction Solvate) and the like mentioned inKautschuk Gummi Kunststoffe 52 (12) 799 (1999), and RAE (ResidualAromatic Extracts).

Examples of the liquid rubber include, but are not limited to, liquidpolybutadiene and liquid styrene-butadiene rubber.

Examples of the resin include, but are not limited to, an aromaticpetroleum resin, a coumarone-indene resin, a terpene-based resin, arosin derivative (including a wood oil resin), tall oil, a derivative oftall oil, a rosin ester resin, a natural or synthetic terpene resin, analiphatic hydrocarbon resin, an aromatic hydrocarbon resin, a mixedaliphatic/aromatic hydrocarbon resin, a coumarin-indene resin, a phenolresin, a p-tert-butylphenol-acetylene resin, a phenol-formaldehyderesin, a xylene-formaldehyde resin, a monoolefin oligomer, a diolefinoligomer, an aromatic hydrocarbon resin, an aromatic petroleum resin, ahydrogenated aromatic hydrocarbon resin, a cyclic aliphatic hydrocarbonresin, a hydrogenated hydrocarbon resin, a hydrocarbon resin, ahydrogenated wood oil resin, a hydrogenated oil resin, and an ester of ahydrogenated oil resin and a monofunctional or polyfunctional alcohol.

One of these resins may be singly used, or two or more of these may beused together. When hydrogenated, all unsaturated groups may behydrogenated, or some may be left not hydrogenated.

The amount to be added of at least any one selected from the groupconsisting of an extender oil, a liquid rubber and a resin is notlimited, and is preferably 1 to 60 parts by mass, more preferably 10 to60 parts by mass, and further preferably 15 to 37.5 parts by mass basedon 100 parts by mass of the conjugated diene-based polymer of thepresent embodiment.

(Desolvation Step)

As a method for obtaining the conjugated diene-based polymer of thepresent embodiment from the polymer solution, any of know methods can beemployed. Examples of the method include a method in which theconjugated diene-based polymer is filtered after separating the solventby steam stripping or the like, and the resultant is dehydrated anddried to obtain the conjugated diene-based polymer, a method in whichthe solution is concentrated in a flushing tank, and the resultant isdevolatilized by using a bent extruder or the like, and a method inwhich the solution is directly devolatilized by using a drum dryer orthe like.

[Rubber Composition]

A rubber composition of the present embodiment contains a rubbercomponent, and 5.0 parts by mass or more and 150 parts by mass or lessof a filler based on 100 parts by mass of the rubber component.

From the viewpoints of fuel efficiency performance, processability andimprovement of abrasion resistance, the rubber component contains, basedon a total amount (100% by mass) of the rubber component, 10% by mass ormore of the above-described conjugated diene-based polymer of thepresent embodiment, or the extended conjugated diene-based polymer ofthe present embodiment.

The filler preferably contains a silica-based inorganic filler.

If a silica-based inorganic filler is dispersed in the rubbercomposition of the present embodiment, the rubber composition tends tobe more excellent in processability obtained when used for obtaining avulcanizate and tends to be more excellent in balance between a lowhysteresis loss property and wet skid resistance, abrasion resistanceand fracture strength when in the form of a vulcanizate.

Also when the rubber composition of the present embodiment is to be usedin application to a vulcanized rubber such as a tire, a vehiclecomponent such as an anti-vibration rubber, or shoes, a silica-basedinorganic filler is preferably contained.

In the rubber composition of the present embodiment, a rubber-likepolymer different from the conjugated diene-based polymer of the presentembodiment (hereinafter simply referred to as the “rubber-like polymer”)may be contained in combination with the conjugated diene-based polymerof the present embodiment.

Examples of such a rubber-like polymer include, but are not limited to,a conjugated diene-based polymer or a hydrogenated product thereof, arandom copolymer of a conjugated diene-based compound and a vinylaromatic compound, or a hydrogenated product thereof, a block copolymerof a conjugated diene-based compound and a vinyl aromatic compound, or ahydrogenated product thereof, a non-diene-based polymer and a naturalrubber.

Specific examples of the rubber-like polymer include, but are notlimited to, a butadiene rubber or a hydrogenated product thereof, anisoprene rubber or a hydrogenated product thereof, styrene-basedelastomers such as a styrene-butadiene rubber or a hydrogenated productthereof, and a styrene-butadiene block copolymer or a hydrogenatedproduct thereof, a styrene-isoprene block copolymer or a hydrogenatedproduct thereof, and an acrylonitrile-butadiene rubber or a hydrogenatedproduct thereof.

Examples of the non-diene-based polymer include, but are not limited to,olefin-based elastomers such as an ethylene-propylene rubber, anethylene-propylene-diene rubber, an ethylene-butene-diene rubber, anethylene-butene rubber, an ethylene-hexene rubber and an ethylene-octenerubber, a butyl rubber, a brominated butyl rubber, an acrylic rubber, afluorine rubber, a silicone rubber, a chlorinated polyethylene rubber,an epichlorohydrin rubber, an α,β-unsaturated nitrile-acrylic acidester-conjugated diene copolymer rubber, a urethane rubber and apolysulfide rubber.

Examples of the natural rubber include, but are not limited to, smokedsheets of RSS Nos. 3 to 5, SMR and epoxidized natural rubber.

The above-described various rubber-like polymers may be in the form of amodified rubber imparted with a functional group having polarity such asa hydroxyl group or an amino group. For use in a tire, a butadienerubber, an isoprene rubber, a styrene-butadiene rubber, a natural rubberand a butyl rubber are preferably used.

The weight average molecular weight of the rubber-like polymer is, fromthe viewpoint of balance between performance and processingcharacteristics, preferably 2,000 or more and 2,000,000 or less, andmore preferably 5,000 or more and 1,500,000 or less. Besides, arubber-like polymer having a low molecular weight, namely, what iscalled a liquid rubber, can be used. One of these rubber-like polymersmay be singly used, or two or more of these may be used together.

In the rubber composition containing the conjugated diene-based polymerof the present embodiment and the rubber-like polymer, a content ratio(in a mass ratio) of the conjugated diene-based polymer of the presentembodiment to the rubber-like polymer is, in terms of (the conjugateddiene-based polymer of the present embodiment/the rubber-like polymer),preferably 10/90 or more and 100/0 or less, more preferably 20/80 ormore and 90/10 or less, and further preferably 50/50 or more and 80/20or less.

Accordingly, the rubber component contained in the rubber compositioncontains, based on the total amount (100 parts by mass) of the rubbercomponent, the conjugated diene-based polymer of the present embodimentin an amount of preferably 10 parts by mass or more and 100 parts bymass or less, more preferably 20 parts by mass or more and 90 parts bymass or less, and further preferably 50 parts by mass or more and 80parts by mass or less.

If the content ratio of (the conjugated diene-based polymer of thepresent embodiment/the rubber-like polymer) falls in the above-describedrange, when in the form of a vulcanizate, balance between a lowhysteresis loss property and wet skid resistance is excellent, abrasionresistance is excellent, and fracture strength is good.

Examples of the filler contained in the rubber composition of thepresent embodiment include, but are not limited to, a silica-basedinorganic filler, carbon black, a metal oxide, and a metal hydroxide.Among these, a silica-based inorganic filler is preferred.

One of these fillers may be singly used, or two or more of these may beused together.

A content of the filler in the rubber composition of the presentembodiment is 5.0 parts by mass or more and 150 parts by mass or less,preferably 20 parts by mass or more and 100 parts by mass or less, andfurther preferably 30 parts by mass or more and 90 parts by mass or lessbased on 100 parts by mass of the rubber component containing theconjugated diene-based polymer of the present embodiment.

From the viewpoint of exhibiting the effect of the filler addition, thecontent of the filler is 5.0 parts by mass or more, and from theviewpoint that the filler is sufficiently dispersed to attainpractically sufficient processability and mechanical strength of therubber composition, the content is 150 parts by mass or less.

The silica-based inorganic filler is not especially limited, any ofknown fillers can be used, a solid particle containing SiO₂ or Si₃Al asa constituent unit is preferred, and a solid particle containing SiO₂ orSi₃Al as a principal component of a constituent unit is more preferred.Here, the principal component refers to a component contained in thesilica-based inorganic filler in an amount of 50% by mass or more,preferably 70% by mass or more, and more preferably 80% by mass or more.

Examples of the silica-based inorganic filler include, but are notlimited to, silica, clay, talc, mica, diatomite, wollastonite,montmorillonite, zeolite and inorganic fibrous substances such as glassfiber.

Besides, examples include a silica-based inorganic filler having ahydrophobized surface, and a mixture of a silica-based inorganic fillerand an inorganic filler excluding silica. Among these, from theviewpoint of strength and abrasion resistance, silica and glass fiberare preferred, and silica is more preferred. Examples of the silicainclude dry silica, wet silica and synthetic silicate silica. Amongthese silica, wet silica is preferred from the viewpoint that it isexcellent in the effect of improving fracture characteristics andbalance in wet skid resistance.

From the viewpoint of obtaining practically good abrasion resistance andfracture characteristics of the rubber composition, a nitrogenadsorption specific surface area, obtained by the BET adsorption method,of the silica-based inorganic filler is preferably 100 m²/g or more and300 m²/g or less, and more preferably 170 m²/g or more and 250 m²/g orless. Besides, a silica-based inorganic filler having a comparativelysmall specific surface area (for example, a specific surface area of 200m²/g or less) and a silica-based inorganic filler having a comparativelylarge specific surface area (for example, 200 m²/g or more) can be usedin combination if necessary.

If a silica-based inorganic filler having a comparatively large specificsurface area (of, for example, 200 m²/g or more) is used in particular,the conjugated diene-based polymer of the present embodiment tends to beimproved in dispersibility of silica, and be effective particularly inimprovement of abrasion resistance, and be capable of well-balanced ingood fracture characteristics and a low hysteresis loss property.

A content of the silica-based inorganic filler in the rubber compositionof the present embodiment is preferably 5.0 parts by mass or more and150 parts by mass or less, more preferably 20 parts by mass or more and100 parts by mass or less based on 100 parts by mass of the rubbercomponent containing the conjugated diene-based polymer of the presentembodiment. From the viewpoint of exhibiting the effect of the additionof the silica-based inorganic filler, the content of the silica-basedinorganic filler is 5.0 parts by mass or more, and from the viewpointthat the silica-based inorganic filler is sufficiently dispersed toattain practically sufficient processability and mechanical strength ofthe rubber composition, the content is 150 parts by mass or less.

Examples of the carbon black include, but are not limited to, carbonblacks of SRF, FEF, HAF, ISAF and SAF classes. Among these, a carbonblack having a nitrogen adsorption specific surface area of 50 m²/g ormore and dibutyl phthalate (DBP) oil absorption of 80 mL/100 g or lessis preferred.

A content of the carbon black is preferably 0.5 parts by mass or moreand 100 parts by mass or less, more preferably 3.0 parts by mass or moreand 100 parts by mass or less, and further preferably 5.0 parts by massor more and 50 parts by mass or less based on 100 parts by mass of therubber component containing the conjugated diene-based polymer of thepresent embodiment. From the viewpoint of exhibiting performancesrequired in use as a tire or the like such as dry grip performance andconductivity, the content of the carbon black is preferably 0.5 parts bymass or more, and from the viewpoint of dispersibility, the content ispreferably 100 parts by mass or less.

The metal oxide refers to a solid particle containing a principalcomponent of a constituent unit represented by chemical formula MxOy(wherein M represents a metal atom, and x and y each independentlyrepresent an integer of 1 to 6).

Examples of the metal oxide include, but are not limited to, alumina,titanium oxide, magnesium oxide and zinc oxide.

Examples of the metal hydroxide include, but are not limited to,aluminum hydroxide, magnesium hydroxide and zirconium hydroxide.

The rubber composition of the present embodiment may contain a silanecoupling agent.

The silane coupling agent is preferably a compound that has a functionto make close the interaction between the rubber component and theinorganic filler, has a group having affinity with or a binding propertyto both of the rubber component, and particularly, the silica-basedinorganic filler, and contains, in one molecule, a sulfur bond portionand an alkoxysilyl group or silanol group portion. Examples of such acompound include bis-[3-(triethoxysilyl)-propyl]-tetrasulfide,bis-[3-(triethoxysilyl)-propyl]-disulfide andbis-[2-(triethoxysilyl)-ethyl]-tetrasulfide.

A content of the silane coupling agent is preferably 0.1 parts by massor more and 30 parts by mass or less, more preferably 0.5 parts by massor more and 20 parts by mass or less, and further preferably 1.0 part bymass or more and 15 parts by mass or less based on 100 parts by mass ofthe filler. If the content of the silane coupling agent falls in theaforementioned range, there is a tendency that the effect of theaddition of the silane coupling agent can be more conspicuous.

The rubber composition of the present embodiment may contain a rubbersoftener from the viewpoint of improvement of the processability.

As the rubber softener, a mineral oil or a liquid or low molecularweight synthetic softener is suitably used.

A mineral oil-based rubber softener, which is used for softening,expanding and improving processability of a rubber and is designated asa process oil or an extender oil, is a mixture of an aromatic ring, anaphthene ring and a paraffin chain, and one in which the number ofcarbon atoms of the paraffin chain is 50% or more of the number of allcarbon atoms is designated as a paraffin-based softener, one in whichthe number of carbon atoms of the naphthene ring is 30% or more and 45%or less of the number of all carbon atoms is designated as anaphthene-based softener, and one in which the number of aromatic carbonatoms exceeds 30% of the number of all carbon atoms is designated as anaromatic-based softener.

When the conjugated diene-based polymer of the present embodiment is acopolymer of a conjugated diene compound and an aromatic vinyl compound,a rubber softener to be used is preferably one having an appropriatearomatic content because such a softener tends to fit with thecopolymer.

A content of the rubber softener is preferably 0 part by mass or moreand 100 parts by mass or less, more preferably 10 parts by mass or moreand 90 parts by mass or less, and further preferably 30 parts by mass ormore and 90 parts by mass or less based on 100 parts by mass of therubber component containing the conjugated diene-based polymer of thepresent embodiment. If the content of the rubber softener is 100 partsby mass or less based on 100 parts by mass of the rubber component,there is a tendency that the bleeding out is suppressed and thestickiness of the surface of the rubber composition of the presentembodiment is suppressed.

Examples of a method for mixing the constituent materials of the rubbercomposition of the present embodiment, such as the rubber componentcontaining the conjugated diene-based polymer of the present embodiment,a silica-based inorganic filler, carbon black or another filler, asilane coupling agent, and an additive such as a rubber softener,include, but are not limited to, a melt-kneading method using a generalmixer such as an open roll, a banbury mixer, a kneader, a single shaftscrew extruder, a twin shaft screw extruder or a multi-shaft screwextruder, and a method in which the respective components are melted andmixed followed by removal of a solvent by heating.

Among these methods, the melt-kneading method using a roll, a banburymixer, a kneader or an extruder is preferred from the viewpoint ofproductivity and high kneadability. Besides, either of a method in whichthe constituent materials of the rubber composition of the presentembodiment are kneaded all together or a method in which the materialsare mixed dividedly in plural times is applicable.

The rubber composition of the present embodiment may be a vulcanizedcomposition having been vulcanized with a vulcanizing agent. Examples ofthe vulcanizing agent include, but are not limited to, radicalgenerators such as organic peroxides and azo compounds, oxime compounds,nitroso compounds, polyamine compounds, sulfur and sulfur compounds.

The sulfur compounds include sulfur monochloride, sulfur dichloride,disulfide compounds and high molecular weight polysulfide compounds.

A content of the vulcanizing agent is preferably 0.01 parts by mass ormore and 20 parts by mass or less, and more preferably 0.1 parts by massor more and 15 parts by mass or less based on 100 parts by mass of therubber component containing the conjugated diene-based polymer of thepresent embodiment. As a vulcanizing method, any of known methods isapplicable, and a vulcanization temperature is preferably 120° C. ormore and 200° C. or less, and more preferably 140° C. or more and 180°C. or less.

For the vulcanization, a vulcanization accelerator may be used ifnecessary.

As the vulcanization accelerator, any of known materials can be used,and examples include, but are not limited to, sulphenamide-based,guanidine-based, thiuram-based, aldehyde-amine-based,aldehyde-ammonia-based, thiazole-based, thiourea-based anddithiocarbamate-based vulcanization accelerators.

Besides, examples of a vulcanization aid include, but are not limitedto, zinc oxide and stearic acid.

A content of the vulcanization accelerator is preferably 0.01 parts bymass or more and 20 parts by mass or less, and more preferably 0.1 partsby mass or more and 15 parts by mass or less based on 100 parts by massof the rubber component containing the conjugated diene-based polymer ofthe present embodiment.

The rubber composition of the present embodiment may contain, as long asthe object of the present embodiment is not impaired, various additivessuch as another softener excluding those described above, a filler, aheat resistance stabilizer, an antistatic agent, a weatheringstabilizer, an anti-ageing agent, a colorant and a lubricant.

As another softener, any of known softeners can be used.

Specific examples of another filler include calcium carbonate, magnesiumcarbonate, aluminum sulfate and barium sulfate.

As each of the heat resistance stabilizer, the antistatic agent, theweathering stabilizer, the anti-ageing agent, the colorant and thelubricant, any of known materials can be used.

[Tire]

The rubber composition of the present embodiment is suitably used as arubber composition for a tire. In other words, a tire of the presentembodiment contains the rubber composition of the present embodiment.

The rubber composition for a tire of the present embodiment isapplicable to, but not limited to, various tires such as afuel-efficient tire, an all-season tire, a high-performance tire and astudless tire; and various tire portions such as a tread, a carcass, asidewall and a bead. In particular, since the rubber composition for atire is excellent in the balance between the low hysteresis lossproperty and the wet skid resistance obtained when in the form of avulcanizate and in the abrasion resistance, it is more suitably used asa tread of a fuel-efficient tire or a high-performance tire.

EXAMPLES

The present embodiment will now be described in more detail withreference to specific examples and comparative examples, and it is notedthat the present embodiment is not limited to the following examples andcomparative examples at all.

Various physical properties of the examples and comparative exampleswere measured by the following methods.

In the following examples and comparative examples, a conjugateddiene-based polymer obtained after modification is referred to as the“modified conjugated diene-based polymer”. One obtained before themodification is referred to as the “unmodified conjugated diene-basedpolymer”.

(Physical Property 1) Amount of Bound Styrene

One hundred (100) mg of a modified conjugated diene-based polymer usedas a sample was dissolved in chloroform to be diluted to 100 mL, and theresultant was used as a measurement sample. Based on the amount ofabsorption of a phenyl group of styrene at a UV absorption wavelength(about 254 nm), the amount of bound styrene (% by mass) based on 100% bymass of the sample of the modified conjugated diene-based polymer wasmeasured (spectrophotometer “UV-2450” manufactured by ShimadzuCorporation).

(Physical Property 2) Microstructure of Butadiene Portion (Amount of1,2-Vinyl Bond)

Fifty (50) mg of a modified conjugated diene-based polymer used as asample was dissolved in 10 mL of carbon disulfide, and the resultant wasused as a measurement sample.

A solution cell was used to measure an infrared spectrum in a range of600 to 1000 cm⁻¹, and in accordance with a calculation formula of theHampton method (R. R. Hampton, Analytical Chemistry 21, 923 (1949))based on absorbance at a prescribed wavelength, a microstructure of abutadiene portion, namely, an amount of 1,2-vinyl bond (mol %) wasobtained (Fourier transform infrared spectrophotometer “FT-IR230”manufactured by JASCO Corporation).

(Physical Property 3) Molecular Weight

Measurement Conditions 1: An unmodified conjugated diene-based polymeror a modified conjugated diene-based polymer used as a sample wasmeasured for a chromatogram using a GPC measurement apparatus (tradename “HLC-8320GPC” manufactured by Tosoh Corporation) including a seriesof three columns using a polystyrene-based gel as a filler with an RIdetector (trade name “HLC8020” manufactured by Tosoh Corporation) used,and on the basis of a calibration curve obtained using standardpolystyrene, a weight average molecular weight (Mw), a number averagemolecular weight (Mn) and a molecular weight distribution (Mw/Mn) wereobtained.

As an eluent, THF (tetrahydrofuran) containing 5 mmol/L of triethylaminewas used. As the columns, trade name “TSKguardcolumn Super MP(HZ)-H”manufactured by Tosoh Corporation connected, as a guard column at aprevious stage, to a series of three columns of trade name “TSKgel SuperMultipore HZ-H” manufactured by Tosoh Corporation were used.

Ten (10) mg of a sample for the measurement was dissolved in 10 mL ofTHF to obtain a measurement solution, and 10 μL of the measurementsolution was injected into the GPC measurement apparatus for performingthe measurement under conditions of an oven temperature of 40° C. and aTHF flow rate of 0.35 mL/min.

Among various samples having been subjected to the measurement under theabove-described measurement conditions 1, a sample having a molecularweight distribution (Mw/Mn) less than 1.6 was subjected again to themeasurement under measurement conditions 2 described below. With respectto samples having been subjected to the measurement under themeasurement conditions 1 and found to have a molecular weightdistribution of 1.6 or more, results obtained by the measurement underthe measurement conditions 1 are shown in Tables 1 to 3.

Measurement Conditions 2: An unmodified conjugated diene-based polymeror a modified conjugated diene-based polymer used as a sample wasmeasured for a chromatogram using a GPC measurement apparatus includinga series of three columns using a polystyrene-based gel as a filler, andon the basis of a calibration curve obtained using standard polystyrene,a weight average molecular weight (Mw), and a number average molecularweight (Mn) were obtained.

As an eluent, THF containing 5 mmol/L of triethylamine was used. As thecolumns, a guard column of trade name “TSKguardcolumn Super H-H”manufactured by Tosoh Corporation, and columns of trade names “TSKgelSuperH5000”, “TSKgel SuperH6000”, and “TSKgel SuperH7000” manufacturedby Tosoh Corporation were used.

An RI detector (trade name “HLC8020” manufactured by Tosoh Corporation)was used under conditions of an oven temperature of 40° C. and a THFflow rate of 0.6 mL/min. Ten (10) mg of a sample for the measurement wasdissolved in 20 mL of THF to obtain a measurement solution, and 20 μL ofthe measurement solution was injected into the GPC measurement apparatusfor performing the measurement.

With respect to a sample having been subjected to the measurement underthe measurement conditions 1 and found to have a molecular weightdistribution less than 1.6, results obtained by the measurement underthe measurement conditions 2 are shown in Tables 1 to 3.

(Physical Property 4) Contracting Factor (g′)

A modified conjugated diene-based polymer was used as a sample, and aGPC measurement apparatus (trade name “GPCmax VE-2001” manufactured byMalvern Panalytical Ltd.) including a series of three columns using apolystyrene-based gel as a filler was used. The measurement wasperformed by using three detectors, that is, a light scatteringdetector, an RI detector, and a viscosity detector (trade name “TDA305”manufactured by Malvern Panalytical Ltd.) connected in the stated order,so as to obtain, based on standard polystyrene, an absolute molecularweight from results obtained by the light scattering detector and the RIdetector, and an intrinsic viscosity from results obtained by the RIdetector and the viscosity detector.

A straight-chain polymer was used under assumption of having anintrinsic viscosity [η] of −3.883 M^(0.771), and a contracting factor(g′) was calculated as a ratio in the intrinsic viscosity to eachmolecular weight.

As an eluent, THF containing 5 mmol/L of triethylamine was used.

As the columns, a series of columns of trade names “TSKgel G4000HXL”,“TSKgel G5000HXL” and “TSKgel G6000HXL” manufactured by TosohCorporation were connected and used.

Twenty (20) mg of a sample for the measurement was dissolved in 10 mL ofTHF to obtain a measurement solution, and 100 μL of the measurementsolution was injected into the GPC measurement apparatus for performingthe measurement under conditions of an oven temperature of 40° C. and aTHF flow rate of 1 mL/min.

(Physical Property 5) Mooney Viscosity of Polymer

An unmodified conjugated diene-based polymer or a modified conjugateddiene-based polymer was used as a sample to measure a Mooney viscosityby using a Mooney viscometer (trade name “VR1132” manufactured byUeshima Seisakusho Co., Ltd.) in accordance with JIS K6300 with anL-type rotor used.

A measurement temperature was 110° C. when an unmodified conjugateddiene-based polymer was used as a sample, and was 100° C. when amodified conjugated diene-based polymer was used as a sample.

First, a sample was preheated at the test temperature for 1 minute, therotor was rotated at 2 rpm, and a torque was measured 4 minutes after asa Mooney viscosity (M_(L(1+4))).

(Physical Property 6) Glass Transition Temperature (Tg)

A modified conjugated diene-based polymer was used as a sample, adifferential scanning calorimeter “DSC3200S” manufactured by Mac Sciencewas used to record a DSC curve under flow of helium at 50 mL/min, with atemperature increased from −100° C. at 20° C./min in accordance with ISO22768:2006, and a peak top (an inflection point) of a DSC differentialcurve thus obtained was defined as a glass transition temperature.

(Physical Property 7) Modification Ratio

A modified conjugated diene-based polymer was used as a sample, and themeasurement was performed by applying a characteristic that a modifiedbasic polymer component adsorbs onto a GPC column using a silica-basedgel as a filler.

A modification ratio was obtained by measuring an amount of adsorptiononto a silica-based column based on a difference between a chromatogrammeasured by using a polystyrene-based column and a chromatogram measuredby using a silica-based column obtained from a sample solutioncontaining a sample and low molecular weight internal standardpolystyrene.

Specifically, the measurement was performed as described below.

A sample found to have a molecular weight distribution of 1.6 or more bythe measurement under the measurement conditions 1 of (Physical Property3) was measured under the following measurement conditions 3. A samplefound to have a molecular weight distribution less than 1.6 by themeasurement under the measurement conditions 1 of (Physical Property 3)was measured under the following measurement conditions 4. Results areshown in Tables 1 to 3.

Preparation of Sample Solution: Ten (10) mg of a sample and 5 mg ofstandard polystyrene were dissolved in 20 mL of THF to obtain a samplesolution.

Measurement Conditions 3: GPC measurement conditions usingpolystyrene-based column:

An apparatus of trade name “HLC-8320GPC” manufactured by TosohCorporation was used, THF containing 5 mmol/L of triethylamine was usedas an eluent, and 10 μL of the sample solution was injected into theapparatus to obtain a chromatogram using an RI detector under conditionsof a column oven temperature of 40° C. and a THF flow rate of 0.35mL/min.

As the columns, a series of three columns of trade name “TSKgel SuperMultipore HZ-H” and a guard column of trade name “TSKguardcolumnSuperMP(HZ)-H” manufactured by Tosoh Corporation connected at a previousstage were used.

Measurement Conditions 4: GPC measurement conditions usingpolystyrene-based column:

An apparatus of trade name “HLC-8320GPC” manufactured by TosohCorporation was used, THF containing 5 mmol/L of triethylamine was usedas an eluent, and 20 μL of the sample solution was injected into theapparatus to perform the measurement.

As the columns, a guard column of trade name “TSKguardcolumn Super H-H”manufactured by Tosoh Corporation and columns of trade names “TSKgelSuper H5000”, “TSKgel Super H6000”, and “TSKgel Super H7000”manufactured by Tosoh Corporation were used. A chromatogram was obtainedby performing the measurement by using an RI detector (HLC8020,manufactured by Tosoh Corporation) under conditions of a column oventemperature of 40° C. and a THF flow rate of 0.6 mL/min.

GPC measurement conditions using silica-based column:

An apparatus of trade name “HLC-8320GPC” manufactured by TosohCorporation was used, THF was used as an eluent, and 50 μL of the samplesolution was injected into the apparatus to obtain a chromatogram byusing an RI detector under conditions of a column oven temperature of40° C. and a THF flow rate of 0.5 mL/min. A series of columns of tradenames “Zorbax PSM-1000S”, “PSM-300S” and “PSM-60S”, and a guard columnof trade name “DIOL 4.6×12.5 mm 5 micron” connected at a previous stagewere used.

Calculation Method for Modification Ratio:

Assuming that the whole peak area of the chromatogram obtained by usingthe polystyrene-based column was 100, that a peak area of the sample wasP1, that a peak area of standard polystyrene was P2, that the whole peakarea of the chromatogram obtained by using the silica-based column was100, that a peak area of the sample was P3, and that a peak area ofstandard polystyrene was P4, a modification ratio (%) was obtained inaccordance with the following expression:

Modification ratio (%)=[1−(P2×P3)/(P1×P4)]×100

wherein P1+P2=P3+P4=100.

(Physical Property 8) Branch Number (Bn)

A modified conjugated diene-based polymer was used as a sample, and aGPC measurement apparatus (trade name “GPCmax VE-2001” manufactured byMalvern Panalytical Ltd.) including a series of three columns using apolystyrene-based gel as a filler was used. The measurement wasperformed by using three detectors, that is, a light scatteringdetector, an RI detector, and a viscosity detector (trade name “TDA305”manufactured by Malvern Panalytical Ltd.) connected in the stated order.Based on standard polystyrene, an absolute molecular weight was obtainedfrom results obtained by using the light scattering detector and the RIdetector, and an intrinsic viscosity was obtained from results obtainedby using the RI detector and the viscosity detector.

A straight-chain polymer was used under assumption of having anintrinsic viscosity [η] of −3.883 M^(0.771), and a contracting factor(g′) was calculated as a ratio in the intrinsic viscosity to eachmolecular weight.

Thereafter, the thus obtained contracting factor (g′) was used tocalculate a branch number (Bn) defined as g′=6 Bn/{(Bn+1) (Bn+2)}.

As an eluent, THF containing 5 mmol/L of triethylamine was used.

As the columns, a series of columns of trade names “TSKgel G4000HXL”,“TSKgel G5000HXL” and “TSKgel G6000HXL” manufactured by TosohCorporation were connected and used.

Twenty (20) mg of a sample for the measurement was dissolved in 10 mL ofTHF to obtain a measurement solution, and 100 μL of the measurementsolution was injected into the GPC measurement apparatus for performingthe measurement under conditions of an oven temperature of 40° C. and aTHF flow rate of 1 mL/min.

(Physical Property 9) Molecular Weight (Absolute Molecular Weight)Obtained by GPC-Light Scattering Measurement

A modified conjugated diene-based polymer was used as a sample, and aGPC-light scattering measurement apparatus including a series of threecolumns using a polystyrene-based gel as a filler was used to measure achromatogram for obtaining a weight average molecular weight (Mw-i)(also designated as an “absolute molecular weight”) based on theviscosity of a solution and a light scattering method.

As an eluent, a mixed solution of tetrahydrofuran and triethylamine (THFin TEA: prepared by mixing 5 mL of triethylamine in 1 L oftetrahydrofuran) was used.

As the columns, a series of a guard column of trade name “TSKguardcolumnHHR-H” manufactured by Tosoh Corporation, and columns of trade names“TSKgel G6000HHR”, “TSKgel G5000HHR”, and “TSKgel G4000HHR” wereconnected and used.

A GPC-light scattering measurement apparatus (trade name “ViscotekTDAmax” manufactured by Malvern Panalytical Ltd.) was used underconditions of an oven temperature of 40° C. and a THF flow rate of 1.0mL/min.

Ten (10) mg of a sample for measurement was dissolved in 20 mL of THF toobtain a measurement solution, and 200 μL of the measurement solutionwas injected into the GPC measurement apparatus for the measurement.

(Example 1) Modified Conjugated Diene-Based Polymer (Sample 1)

Two tank pressure vessels, each of which is a stirrer-equipped tankreactor having an internal volume of 10 L and a ratio (L/D) of internalheight (L) and diameter (D) of 4.0, having an inlet at a bottom and anoutlet at a top, and equipped with a stirrer and a temperaturecontrolling jacket, were connected to each other as polymerizationreactors.

1,3-Butadiene, styrene and n-hexane, from which a water content had beenprecedently removed were mixed under conditions of 18.6 g/min, 10.0g/min and 175.2 g/min, respectively. In a static mixer provided in themiddle of a pipe for supplying the thus obtained mixed solution to theinlet of the reactor, n-butyllithium to be used for residual impurityinactivation was added and mixed in an amount of 0.103 mmol/min, and theresultant was continuously supplied to the bottom of the reactor.Besides, 2,2-bis(2-oxolanyl)propane used as a polar material andn-butyllithium used as a polymerization initiator were supplied, atrates of respectively 0.081 mmol/min and 0.143 mmol/min, to the bottomof the first reactor in which materials were vigorously mixed by thestirrer, and the internal temperature of the reactor was kept at 67° C.

The thus obtained polymer solution was continuously taken out from thetop of the first reactor to be continuously supplied to the bottom ofthe second reactor for continuing the reaction at 70° C., and theresultant was further supplied to a static mixer from the top of thesecond reactor. When the polymerization was sufficiently stabilized,trimethoxy(4-vinylphenyl)silane (shown as “BS-1” in a table) used as abranching agent was added at a rate of 0.0190 mmol/min from the bottomof the second reactor. When the polymerization reaction and thebranching reaction were stabilized, a small amount of a conjugateddiene-based polymer solution prior to addition of a modifier was takenout, an antioxidant (BHT) was added thereto in an amount of 0.2 g per100 g of the polymer, then the solvent was removed, and a Mooneyviscosity at 110° C. and various molecular weights were measured. Theother physical properties are also shown in Table 1.

Next, to the polymer solution flowing out of an outlet of the reactor,2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane(shown as “A” in the table) was added, as a modifier, continuously at arate of 0.0360 mmol/min, and the resultant was mixed by using a staticmixer for performing a modification reaction. Here, a time until theaddition of the modifier to the polymer solution flowing out of theoutlet of the reactor was 4.8 min, the temperature was 68° C., and adifference between the temperature in the polymerizing step and thetemperature until the addition of the modifier was 2° C. To the polymersolution having been subjected to the modification reaction, anantioxidant (BHT) was added in an amount of 0.2 g per 100 g of thepolymer continuously at 0.055 g/min (n-hexane solution) to complete themodification reaction. Simultaneously with the antioxidant, an oil (JOMOProcess NC 140, manufactured by JX Nippon Oil & Energy Corporation) wascontinuously added in an amount of 37.5 g per 100 g of the polymer, andthe resultant was mixed by using a static mixer. The solvent was removedby steam stripping, and thus, a modified conjugated diene-based polymer(sample 1) was obtained. Physical properties of the sample 1 are shownin Table 1.

(Example 2) Modified Conjugated Diene-Based Polymer (Sample 2)

A modified conjugated diene-based polymer (sample 2) was obtained in thesame manner as in Example 1 except that the modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totris(3-trimethoxysilylpropyl)amine (shown as “B” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 2 are shown in Table 1.

(Example 3) Modified Conjugated Diene-Based Polymer (Sample 3)

A modified conjugated diene-based polymer (sample 3) was obtained in thesame manner as in Example 1 except that the modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0190 mmol/min. Physical properties of the sample 3 are shown in Table1.

(Example 4) Modified Conjugated Diene-Based Polymer (Sample 4)

A modified conjugated diene-based polymer (sample 4) was obtained in thesame manner as in Example 1 except that the modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 4 are shown in Table1.

(Example 5) Modified Conjugated Diene-Based Polymer (Sample 5)

A modified conjugated diene-based polymer (sample 5) was obtained in thesame manner as in Example 1 except that the branching agent was changedfrom trimethoxy(4-vinylphenyl)silane todimethylmethoxy(4-vinylphenyl)silane (shown as “BS-2” in the table), andthat the amount thereof to be added was changed to 0.0350 mmol/min.Physical properties of the sample 5 are shown in Table 1.

(Example 6) Modified Conjugated Diene-Based Polymer (Sample 6)

A modified conjugated diene-based polymer (sample 6) was obtained in thesame manner as in Example 1 except that the branching agent was changedfrom trimethoxy(4-vinylphenyl)silane todimethylmethoxy(4-vinylphenyl)silane (shown as “BS-2” in the table),that the amount thereof to be added was changed to 0.0350 mmol/min, thatthe modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totris(3-trimethoxysilylpropyl)amine (shown as “B” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 6 are shown in Table 1.

(Example 7) Modified Conjugated Diene-Based Polymer (Sample 7)

A modified conjugated diene-based polymer (sample 7) was obtained in thesame manner as in Example 1 except that the branching agent was changedfrom trimethoxy(4-vinylphenyl)silane todimethylmethoxy(4-vinylphenyl)silane (shown as “BS-2” in the table),that the amount thereof to be added was changed to 0.0350 mmol/min, thatthe modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 7 are shown in Table1.

(Example 8) Modified Conjugated Diene-Based Polymer (Sample 8)

A modified conjugated diene-based polymer (sample 8) was obtained in thesame manner as in Example 1 except that the branching agent was changedfrom trimethoxy(4-vinylphenyl)silane to1,1-bis(4-dimethylmethoxysilyl)phenyl)ethylene (shown as “BS-3” in thetable), and that the amount thereof to be added was changed to 0.0120mmol/min. Physical properties of the sample 8 are shown in Table 1.

(Example 9) Modified Conjugated Diene-Based Polymer (Sample 9)

A modified conjugated diene-based polymer (sample 9) was obtained in thesame manner as in Example 1 except that the branching agent was changedfrom trimethoxy(4-vinylphenyl)silane to1,1-bis(4-dimethylmethoxysilyl)phenyl)ethylene (shown as “BS-3” in thetable), that the amount thereof to be added was changed to 0.0120mmol/min, that the modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totris(3-trimethoxysilylpropyl)amine (shown as “B” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 9 are shown in Table 1.

(Example 10) Modified Conjugated Diene-Based Polymer (Sample 10)

A modified conjugated diene-based polymer (sample 10) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane to1,1-bis(4-dimethylmethoxysilyl)phenyl)ethylene (shown as “BS-3” in thetable), that the amount thereof to be added was changed to 0.0120mmol/min, that the modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 10 are shown in Table1.

(Example 11) Modified Conjugated Diene-Based Polymer (Sample 11)

A modified conjugated diene-based polymer (sample 11) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane to1,1-bis(4-trimethoxysilylphenyl)ethylene (shown as “BS-4” in the table),and that the amount thereof to be added was changed to 0.0210 mmol/min.Physical properties of the sample 11 are shown in Table 2.

(Example 12) Modified Conjugated Diene-based Polymer (Sample 12)

A modified conjugated diene-based polymer (sample 12) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane to1,1-bis(4-trimethoxysilylphenyl)ethylene (shown as “BS-4” in the table),that the amount thereof to be added was changed to 0.0210 mmol/min, thatthe modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totris(3-trimethoxysilylpropyl)amine (shown as “B” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 12 are shown in Table 2.

(Example 13) Modified Conjugated Diene-Based Polymer (Sample 13)

A modified conjugated diene-based polymer (sample 13) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane to1,1-bis(4-trimethoxysilylphenyl)ethylene (shown as “BS-4” in the table),that the amount thereof to be added was changed to 0.0210 mmol/min, thatthe modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 13 are shown in Table2.

(Example 14) Modified Conjugated Diene-Based Polymer (Sample 14)

A modified conjugated diene-based polymer (sample 14) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane totrichloro(4-vinylphenyl)silane (shown as “BS-5” in the table). Physicalproperties of the sample 14 are shown in Table 2.

(Example 15) Modified Conjugated Diene-Based Polymer (Sample 15)

A modified conjugated diene-based polymer (sample 15) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane totrichloro(4-vinylphenyl)silane (shown as “BS-5” in the table), that themodifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totris(3-trimethoxysilylpropyl)amine (shown as “B” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 15 are shown in Table 2.

(Example 16) Modified Conjugated Diene-Based Polymer (Sample 16)

A modified conjugated diene-based polymer (sample 16) was obtained inthe same manner as in Example 1 except that the branching agent waschanged from trimethoxy(4-vinylphenyl)silane totrichloro(4-vinylphenyl)silane (shown as “BS-5” in the table), that themodifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 16 are shown in Table2.

(Example 17) Modified Conjugated Diene-Based Polymer (Sample 17)

A modified conjugated diene-based polymer (sample 17) was obtained inthe same manner as in Example 1 except that the amount oftrimethoxy(4-vinylphenyl)silane (shown as “BS-1” in the table) to beadded as the branching agent was changed to 0.0100 mmol/min, that themodifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 17 are shown in Table2.

(Example 18) Modified Conjugated Diene-Based Polymer (Sample 18)

A modified conjugated diene-based polymer (sample 18) was obtained inthe same manner as in Example 1 except that the amount oftrimethoxy(4-vinylphenyl)silane (shown as “BS-1” in the table) to beadded as the branching agent was changed to 0.0250 mmol/min, that themodifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 18 are shown in Table2.

(Example 19) Modified Conjugated Diene-Based Polymer (Sample 19)

A modified conjugated diene-based polymer (sample 19) was obtained inthe same manner as in Example 1 except that the amount oftrimethoxy(4-vinylphenyl)silane (shown as “BS-1” in the table) to beadded as the branching agent was changed to 0.0350 mmol/min, that themodifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0160 mmol/min. Physical properties of the sample 19 are shown in Table2.

(Example 20) Conjugated Diene-Based Polymer (Sample 20)

A conjugated diene-based polymer (sample 20) was obtained in the samemanner as in Example 1 except that the modifier was changed from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane to acoupling agent of tetraethoxysilane (shown as “D” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 20 are shown in Table 2.

(Comparative Example 1) Modified Conjugated Diene-Based Polymer (Sample21)

Two tank pressure vessels, each of which is a stirrer-equipped tankreactor having an internal volume of 10 L and a ratio (L/D) of internalheight (L) and diameter (D) of 4.0, having an inlet at a bottom and anoutlet at a top, and equipped with a stirrer and a temperaturecontrolling jacket, were connected to each other as polymerizationreactors.

1,3-Butadiene, styrene and n-hexane, from which a water content had beenprecedently removed were mixed under conditions of 18.6 g/min, 10.0g/min and 175.2 g/min, respectively. In a static mixer provided in themiddle of a pipe for supplying the thus obtained mixed solution to theinlet of the reactor, n-butyllithium to be used for residual impurityinactivation was added and mixed in an amount of 0.103 mmol/min, and theresultant was continuously supplied to the bottom of the reactor.Besides, 2,2-bis(2-oxolanyl)propane used as a polar material andn-butyllithium used as a polymerization initiator were supplied, atrates of respectively 0.081 mmol/min and 0.143 mmol/min, to the bottomof the first reactor in which materials were vigorously mixed by thestirrer, and the internal temperature of the reactor was kept at 67° C.

The thus obtained polymer solution was continuously taken out from thetop of the first reactor to be continuously supplied to the bottom ofthe second reactor for continuing the reaction at 70° C., and theresultant was further supplied to a static mixer from the top of thesecond reactor. When the polymerization was sufficiently stabilized, asmall amount of a polymer solution prior to addition of a modifier wastaken out, an antioxidant (BHT) was added thereto in an amount of 0.2 gper 100 g of the polymer, then the solvent was removed, and a Mooneyviscosity at 110° C. and various molecular weights were measured. Theother physical properties are also shown in Table 3.

Next, to the polymer solution flowing out of an outlet of the reactor,2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane(shown as “A” in the table) was added, as a modifier, continuously at arate of 0.0360 mmol/min, and the resultant was mixed by using a staticmixer for performing a modification reaction. Here, a time until theaddition of the modifier to the polymer solution flowing out of theoutlet of the reactor was 4.8 min, the temperature was 68° C., and adifference between the temperature in the polymerizing step and thetemperature until the addition of the modifier was 2° C. To the polymersolution having been subjected to the modification reaction, anantioxidant (BHT) was added in an amount of 0.2 g per 100 g of thepolymer continuously at 0.055 g/min (n-hexane solution) to complete themodification reaction. Simultaneously with the antioxidant, an oil (JOMOProcess NC 140, manufactured by JX Nippon Oil & Energy Corporation) wascontinuously added in an amount of 37.5 g per 100 g of the polymer, andthe resultant was mixed by using a static mixer. The solvent was removedby steam stripping, and thus, a modified conjugated diene-based polymer(sample 21) was obtained. Physical properties of the sample 21 are shownin Table 3.

(Comparative Example 2) Modified Conjugated Diene-Based Polymer (Sample22)

A modified conjugated diene-based polymer (sample 22) was obtained inthe same manner as in Comparative Example 1 except that the modifier waschanged from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totris(3-trimethoxysilylpropyl)amine (shown as “B” in the table”), andthat the amount thereof to be added was changed to 0.0250 mmol/min.Physical properties of the sample 22 are shown in Table 3.

(Comparative Example 3) Branched Modified Diene-Based Polymer (Sample23)

A modified conjugated diene-based polymer (sample 23) was obtained inthe same manner as in Comparative Example 1 except that the modifier waschanged from2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane totetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (shown as “C” inthe table”), and that the amount thereof to be added was changed to0.0190 mmol/min. Physical properties of the sample 23 are shown in Table3.

(Comparative Example 4) Branched Modified Diene-Based Polymer (Sample24)

A modified conjugated diene-based polymer (sample 24) was obtained inthe same manner as in Comparative Example 1 except that the amount of2,2-bis(2-oxolanyl)propane to be added as the polar material was changedto a rate of 0.105 mmol/min, that the amount of n-butyllithium to beadded as the polymerization initiator was changed to a rate of 0.188mmol/min, that the amount of trimethoxy(4-vinylphenyl)silane (shown as“BS-1” in the table) to be added as the branching agent was changed to0.0350 mmol/min, and that the amount of2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane to beadded as the modifier was changed to 0.0510 mmol/min. Physicalproperties of the sample 24 are shown in Table 3.

(Comparative Example 5) Modified Conjugated Diene-Based Polymer (Sample25)

One tank pressure vessel, which is a stirrer-equipped tank reactorhaving an internal volume of 0.5 L and a ratio (L/D) of internal height(L) and diameter (D) of 4.0, having an inlet at a bottom and an outletat a top, equipped with a stirrer and a temperature controlling jacket,and two tank pressure vessels, each of which is a stirrer-equipped tankreactor having an internal volume of 10 L and a ratio (L/D) of internalheight (L) and diameter (D) of 4.0, having an inlet at a bottom and anoutlet at a top, and equipped with a stirrer and a temperaturecontrolling jacket, were connected to one another, namely, threereactors in total were connected, as polymerization reactors.

n-Hexane, from which a water content had been precedently removed,2,2-bis(2-oxolanyl)propane used as the polar material, n-butyllithiumused as the polymerization initiator, and n-butyllithium to be used forresidual impurity inactivation were added under conditions of 175.2g/min, at a rate of 0.081 mmol/min, at a rate of 0.143 mmol/min, and0.103 mmol/min, respectively, and trimethoxy(4-vinylphenyl)silane (shownas “BS-1” in the table”) was added thereto as the branching agent at arate of 0.0190 mmol/min. The resultant was vigorously mixed by thestirrer, and the internal temperature of the reactor was kept at 67° C.to construct a polymer block component.

The thus obtained polymer solution was continuously taken out from thetop of the first reactor, and continuously supplied to the bottom of thesecond reactor, and 1,3-butadiene and styrene, from which a watercontent had been precedently removed were supplied from the bottom ofthe second reactor under conditions of 18.6 g/min and 10.0 g/min,respectively, and mixed.

The reaction was continued at 70° C., and the resultant polymer solutionwas continuously taken out from the top of the second reactor,continuously supplied to the bottom of the third reactor, and furthersupplied to a static mixer from the top of the third reactor. The thusobtained mixed solution was supplied to a static mixer provided in themiddle of a pipe for supply to the inlet of the third reactor. When thepolymerization was sufficiently stabilized, a small amount of a polymersolution prior to addition of a modifier was taken out, an antioxidant(BHT) was added thereto in an amount of 0.2 g per 100 g of the polymer,then the solvent was removed, and a Mooney viscosity at 110° C. andvarious molecular weights were measured. The other physical propertiesare also shown in Table 3.

Next, to the polymer solution flowing out of an outlet of the reactor,2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane(shown as “A” in the table) was added, as a modifier, continuously at arate of 0.0360 mmol/min, and the resultant was mixed by using a staticmixer for performing a modification reaction. Here, a time until theaddition of the modifier to the polymer solution flowing out of theoutlet of the reactor was 4.8 min, the temperature was 68° C., and adifference between the temperature in the polymerizing step and thetemperature until the addition of the modifier was 2° C. To the polymersolution having been subjected to the modification reaction, anantioxidant (BHT) was added in an amount of 0.2 g per 100 g of thepolymer continuously at 0.055 g/min (n-hexane solution) to complete themodification reaction. Simultaneously with the antioxidant, an oil (JOMOProcess NC 140, manufactured by JX Nippon Oil & Energy Corporation) wascontinuously added in an amount of 37.5 g per 100 g of the polymer, andthe resultant was mixed by using a static mixer. The solvent was removedby steam stripping, and thus, a modified conjugated diene-based polymer(sample 25) was obtained. Physical properties of the sample 25 are shownin Table 3.

TABLE 1 Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5Modified Conjugated Diene-based Polymer (Sample No.) 1 2 3 4 5 Polymeri-Butadiene (g/min) 18.6 18.6 18.6 18.6 18.6 zation Styrene (g/min) 10.010.0 10.0 10.0 10.0 Conditions n-Hexane (g/min) 175.2 175.2 175.2 175.2175.2 Polymerization Temperature (° C.) 70 70 70 70 70 n-Butyllithiumfor Treatment (mmol/min) 0.103 0.103 0.103 0.103 0.103 n-Butyllithium ofPolymerization Initiator (mmol/min) 0.143 0.143 0.143 0.143 0.143 Amountof Polar Material Added (mmol/min) 0.081 0.081 0.081 0.081 0.081Branching Type BS-1 BS-1 BS-1 BS-1 BS-2 Agent Amount Added (mmol/min)0.0190 0.0190 0.0190 0.0190 0.0350 Modifier Type A B C C A Amount Added(mmol/min) 0.0360 0.0250 0.0190 0.0160 0.0360 Physical Conjugated(Physical Property 3) Weight Average (10⁴ g/mol) 63.9 63.9 63.9 63.960.3 Properties Diene- Molecular Weight based (Physical Property 3)Number Average (10⁴ g/mol) 33.1 33.1 33.1 33.1 32.2 Polymer MolecularWeight (Physical Property 4) Mooney Viscosity 92.1 92.1 92.1 92.1 88.2(110° C.) (Physical Property 3) Mw/Mn 1.93 1.93 1.93 1.93 1.87 Modified(Physical Property 1) Amount of Bound (mass %) 35 35 35 35 35 ConjugatedStyrene Diene- (Physical Property 2) Amount of Bound (mol %) 40 40 40 4040 based Vinyl (Amount of 1,2-Bond) Polymer (Physical Property 3) WeightAverage (10⁴ g/mol) 92.0 96.0 105.3 106.0 86.8 Molecular Weight(Physical Property 3) Number Average (10⁴ g/mol) 46.7 48.7 53.4 54.643.8 Molecular Weight (Physical Property 3) Mw/Mn 1.97 1.97 1.97 1.941.98 (Physical Property 4) Contracting Factor (g′) 0.52 0.40 0.32 0.260.53 (Physical Property 5) Mooney Viscosity of 83 83 83 82 79 Polymer(100° C.) (Physical Property 6) Glass Transition (° C.) −23 −23 −23 −23−23 Temperature (Physical Property 7) Modification Ratio (%) 88 86 86 8285 (Physical Property 8) Branch Number Bn per molecule 8.7 12.0 15.820.0 8.0 (Physical Property 9) Absolute Molecular (10⁴ Daltons) 144 170186 281 136 Weight (Mw-i) Exam- Exam- Exam- Exam- Exam- ple 6 ple 7 ple8 ple 9 ple 10 Modified Conjugated Diene-based Polymer (Sample No.) 6 78 9 10 Polymeri- Butadiene (g/min) 18.6 18.6 18.6 18.6 18.6 zationStyrene (g/min) 10.0 10.0 10.0 10.0 10.0 Conditions n-Hexane (g/min)175.2 175.2 175.2 175.2 175.2 Polymerization Temperature (° C.) 70 70 7070 70 n-Butyllithium for Treatment (mmol/min) 0.103 0.103 0.103 0.1030.103 n-Butyllithium of Polymerization Initiator (mmol/min) 0.143 0.1430.143 0.143 0.143 Amount of Polar Material Added (mmol/min) 0.081 0.0810.081 0.081 0.081 Branching Type BS-2 BS-2 BS-3 BS-3 BS-3 Agent AmountAdded (mmol/min) 0.0350 0.0350 0.0120 0.0120 0.0120 Modifier Type B C AB C Amount Added (mmol/min) 0.0250 0.0160 0.0360 0.0250 0.0160 PhysicalConjugated (Physical Property 3) Weight Average (10⁴ g/mol) 60.3 60.374.5 74.5 74.5 Properties Diene- Molecular Weight based (PhysicalProperty 3) Number Average (10⁴ g/mol) 32.2 32.2 37.8 37.8 37.8 PolymerMolecular Weight (Physical Property 4) Mooney Viscosity 88.2 88.2 99.199.1 99.1 (110° C.) (Physical Property 3) Mw/Mn 1.87 1.87 1.97 1.97 1.97Modified (Physical Property 1) Amount of Bound (mass %) 35 35 35 35 35Conjugated Styrene Diene- (Physical Property 2) Amount of Bound (mol %)40 40 40 40 40 based Vinyl (Amount of 1,2-Bond) Polymer (PhysicalProperty 3) Weight Average (10⁴ g/mol) 90.6 99.4 115.0 121.0 135.0Molecular Weight (Physical Property 3) Number Average (10⁴ g/mol) 46.551.5 57.2 62.4 69.6 Molecular Weight (Physical Property 3) Mw/Mn 1.951.93 2.01 1.94 1.94 (Physical Property 4) Contracting Factor (g′) 0.450.37 0.28 0.21 0.18 (Physical Property 5) Mooney Viscosity of 84 82 8184 82 Polymer (100° C.) (Physical Property 6) Glass Transition (° C.)−23 −23 −23 −23 −23 Temperature (Physical Property 7) Modification Ratio(%) 84 81 82 84 85 (Physical Property 8) Branch Number Bn per molecule10.0 13.0 18.0 26.0 30.0 (Physical Property 9) Absolute Molecular (10⁴Daltons) 160 176 160 203 334.8 Weight (Mw-i)

TABLE 2 Exam- Exam- Exam- Exam- Exam- ple 11 ple 12 ple 13 ple 14 ple 15Modified Conjugated Diene-based Polymer (Sample No.) 11 12 13 14 15Polymeri- Butadiene (g/min) 18.6 18.6 18.6 18.6 18.6 zation Styrene(g/min) 10.0 10.0 10.0 10.0 10.0 Conditions n-Hexane (g/min) 175.2 175.2175.2 175.2 175.2 Polymerization Temperature (° C.) 70 70 70 70 70n-Butyllithium for Treatment (mmol/min) 0.103 0.103 0.103 0.103 0.103n-Butyllithium of Polymerization Initiator (mmol/min) 0.143 0.143 0.1430.143 0.143 Amount of Polar Material Added (mmol/min) 0.081 0.081 0.0810.081 0.081 Branching Type BS-4 BS-4 BS-4 BS-5 BS-5 Agent Amount Added(mmol/min) 0.0210 0.0210 0.0210 0.0190 0.0190 Modifier Type A B C A BAmount Added (mmol/min) 0.0360 0.0250 0.0160 0.0360 0.0250 PhysicalConjugated (Physical Property 3) Weight Average (10⁴ g/mol) 61.5 61.561.5 63.9 63.9 Properties Diene- Molecular Weight based (PhysicalProperty 3) Number Average (10⁴ g/mol) 31.1 31.1 31.1 33.1 33.1 PolymerMolecular Weight (Physical Property 4) Mooney Viscosity 90.6 90.6 90.692.1 92.1 (110° C.) (Physical Property 3) Mw/Mn 1.98 1.98 1.98 1.93 1.93Modified (Physical Property 1) Amount of (mass %) 35 35 35 35 35Conjugated Bound Styrene Diene- (Physical Property 2) Amount of Bound(mol %) 40 40 40 40 40 based Vinyl (Amount of 1,2-Bond) Polymer(Physical Property 3) Weight Average (10⁴ g/mol) 91.0 94.0 102.3 92.096.0 Molecular Weight (Physical Property 3) Number Average (10⁴ g/mol)46.0 48.2 51.9 46.7 48.7 Molecular Weight (Physical Property 3) Mw/Mn1.98 1.95 1.97 1.97 1.97 (Physical Property 4) Contracting Factor (g′)0.51 0.41 0.35 0.52 0.40 (Physical Property 5) Mooney Viscosity of 82 8384 83 83 Polymer (100° C.) (Physical Property 6) Glass Transition (° C.)−23 −23 −23 −23 −23 Temperature (Physical Property 7) Modification Ratio(%) 82 84 62 88 86 (Physical Property 8) Branch Number Bn per molecule8.5 11.5 14.2 8.7 12.0 (Physical Property 9) Absolute Molecular (10⁴ 135165 184 144 170 Weight (Mw-i) Daltons) Exam- Exam- Exam- Exam- Exam- ple16 ple 17 ple 18 ple 19 ple 20 Modified Conjugated Diene-based Polymer(Sample No.) 16 17 18 19 20 Polymeri- Butadiene (g/min) 18.6 18.6 18.618.6 18.6 zation Styrene (g/min) 10.0 10.0 10.0 10.0 10.0 Conditionsn-Hexane (g/min) 175.2 175.2 175.2 175.2 175.2 PolymerizationTemperature (° C.) 70 70 70 70 70 n-Butyllithium for Treatment(mmol/min) 0.103 0.103 0.103 0.103 0.103 n-Butyllithium ofPolymerization Initiator (mmol/min) 0.143 0.143 0.143 0.143 0.143 Amountof Polar Material Added (mmol/min) 0.081 0.081 0.081 0.081 0.081Branching Type BS-5 BS-1 BS-1 BS-1 BS-1 Agent Amount Added (mmol/min)0.0190 0.0100 0.0250 0.0350 0.0190 Modifier Type C C C C D Amount Added(mmol/min) 0.0190 0.0160 0.0160 0.0160 0.0250 Physical Conjugated(Physical Property 3) Weight Average (10⁴ g/mol) 63.9 55.9 78.6 89.363.9 Properties Diene- Molecular Weight based (Physical Property 3)Number Average (10⁴ g/mol) 33.1 28.5 40.1 45.1 33.1 Polymer MolecularWeight (Physical Property 4) Mooney Viscosity 92.1 88.1 98.1 105.3 92.1(110° C.) (Physical Property 3) Mw/Mn 1.93 1.96 1.96 1.98 1.93 Modified(Physical Property 1) Amount of (mass %) 35 35 35 35 35 Conjugated BoundStyrene Diene- (Physical Property 2) Amount of Bound (mol %) 40 40 40 4040 based Vinyl (Amount of 1,2-Bond) Polymer (Physical Property 3) WeightAverage (10⁴ g/mol) 105.3 98.1 117.0 125.0 95.8 Molecular Weight(Physical Property 3) Number Average (10⁴ g/mol) 53.4 50.6 59.7 62.248.4 Molecular Weight (Physical Property 3) Mw/Mn 1.97 1.94 1.96 2.011.98 (Physical Property 4) Contracting Factor (g′) 0.32 0.38 0.21 0.180.40 (Physical Property 5) Mooney Viscosity of 83 87 90 92 80 Polymer(100° C.) (Physical Property 6) Glass Transition (° C.) −23 −23 −23 −23−23 Temperature (Physical Property 7) Modification Ratio (%) 86 92 75 680 (Physical Property 8) Branch Number Bn per molecule 15.8 12.5 25.330.1 12.0 (Physical Property 9) Absolute Molecular (10⁴ 186 245 320 360158 Weight (Mw-i) Daltons)

TABLE 3 Compar- Compar- Compar- Compar- Compar- ative ative ative ativeative Example 1 Example 2 Example 3 Example 4 Example 5 ModifiedConjugated Diene-based Polymer (Sample No.) 21 22 23 24 25 Polymeri-Butadiene (g/min) 18.6 18.6 18.6 18.6 18.6 zation Styrene (g/min) 10.010.0 10.0 10.0 10.0 Conditions n-Hexane (g/min) 175.2 175.2 175.2 175.2175.2 Polymerization Temperature (° C.) 70 70 70 70 70 n-Butyllithiumfor Treatment (mmol/min) 0.103 0.103 0.103 0.103 0.103 n-Butyllithium ofPolymerization Initiator (mmol/min) 0.143 0.143 0.143 0.188 0.143 Amountof Polar Material Added (mmol/min) 0.081 0.081 0.081 0.105 0.081Branching Type — — — BS-1 BS-1 Agent Amount Added (mmol/min) — — —0.0350 0.0190 Modifier Type A B C A A Amount Added (mmol/min) 0.03600.0250 0.0190 0.0510 0.0360 Physical Conjugated (Physical Property 3)Weight Average (10⁴ g/mol) 48.9 48.9 48.9 18.9 49.0 Properties Diene-Molecular Weight based (Physical Property 3) Number Average (10⁴ g/mol)27.9 27.9 27.9 9.6 28.0 Polymer Molecular Weight (Physical Property 4)Mooney Viscosity 72.5 72.5 72.5 25 72.6 (110° C.) (Physical Property 3)Mw/Mn 1.75 1.75 1.75 1.97 1.75 Modified (Physical Property 1) Amount of(mass %) 35 35 35 35 35 Conjugated Bound Styrene Diene- (PhysicalProperty 2) Amount of Bound Vinyl (mol %) 40 40 40 40 40 based (Amountof 1,2-Bond) Polymer (Physical Property 3) Weight Average (10⁴ g/mol)82.1 94.3 117.4 27.2 82.1 Molecular Weight (Physical Property 3) NumberAverage (10⁴ g/mol) 40.8 47.9 53.4 13.5 40.8 Molecular Weight (PhysicalProperty 3) Mw/Mn 2.01 1.97 1.98 2.01 2.01 (Physical Property 4)Contracting Factor (g′) 0.91 0.74 0.56 0.52 0.91 (Physical Property 5)Mooney Viscosity of 75 83 96 40 75 Polymer (100° C.) (Physical Property6) Glass Transition (° C.) −23 −23 −23 −23 −23 Temperature (PhysicalProperty 7) Modification Ratio (%) 83 86 80 82 83 (Physical Property 8)Branch Number Bn per molecule 2.9 4.6 7.4 8.4 2.9 (Physical Property 9)Absolute Molecular (10⁴ 96 97 142 38 96 Weight (Mw-i) Daltons)

Examples 21 to 40, and Comparative Examples 6 to 10

The samples 1 to 25 shown in Tables 1 to 3 were respectively used as rawmaterial rubbers to obtain rubber compositions respectively containingthe raw material rubbers in accordance with the following composition:

Conjugated diene-based polymer or modified conjugated diene-basedpolymer (each of the samples 1 to 25): 100 parts by mass (excluding oil)

Silica 1 (trade name “Ultrasil 7000GR”, manufactured by Evonik Degussa,nitrogen adsorption specific surface area: 170 m²/g): 50.0 parts by mass

Silica 2 (trade name “Zeosil Premium 200MP” manufactured by Rhodia,nitrogen adsorption specific surface area: 220 m²/g): 25.0 parts by mass

Carbon black (trade name “Seast KH (N339)”, manufactured by Tokai CarbonCo., Ltd.): 5.0 parts by mass

Silane coupling agent: (trade name “Si75”, manufactured by EvonikDegussa, bis(triethoxysilylpropyl)disulfide): 6.0 parts by mass

S-RAE oil (trade name “Process NC140”, manufactured by JX Nippon Oil &Energy Corporation): 37.5 parts by mass

Zinc oxide: 2.5 parts by mass

Stearic acid: 1.0 part by mass

Anti-ageing agent (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine):2.0 parts by mass

Sulfur: 2.2 parts by mass

Vulcanization accelerator 1 (N-cyclohexyl-2-benzothiazylsulfinamide):1.7 parts by mass

Vulcanization accelerator 2 (diphenylguanidine): 2.0 parts by mass

Total: 239.4 parts by mass

The above-described materials were kneaded by the following method toobtain a rubber composition. A closed kneader (having an internal volumeof 0.3 L) equipped with a temperature controller was used to knead, as afirst stage of kneading, the raw material rubber (each of the samples 1to 25), the fillers (silica 1, silica 2 and carbon black), the silanecoupling agent, the process oil, zinc oxide and stearic acid underconditions of a filling ratio of 65% and a rotor rotation speed of 30 to50 rpm. Here, the temperature of the closed kneader was controlled toobtain each rubber composition (compound) at a discharging temperatureof 155 to 160° C.

Next, after cooling the compound obtained as described above to roomtemperature, as a second stage of the kneading, the anti-ageing agentwas added thereto, and the resultant was kneaded again to improvedispersibility of the silica. Also in this case, the dischargingtemperature for the compound was adjusted to 155 to 160° C. by thetemperature control of the mixer. After cooling, as a third stage of thekneading, sulfur and the vulcanization accelerators 1 and 2 were added,and the resultant was kneaded by an open roll set to 70° C. Thereafter,the resultant was molded and vulcanized at 160° C. for 20 minutes by avulcanizing press. The rubber compositions prior to the vulcanization,and the rubber compositions after the vulcanization were evaluated.Specifically, the evaluations were performed as described below. Resultsare shown in Tables 4 to 6.

(Evaluation 1) Mooney Viscosity of Compound

Each compound obtained after the second stage of the kneading and beforethe third stage of the kneading was used as a sample to measure aviscosity by using a Mooney viscometer in accordance with JIS K6300-1after preheating the compound at 130° C. for 1 minute, and afterrotating a rotor for 4 minutes at 2 rpm. The thus obtained viscosity wasshown as an index obtained assuming that a result of Comparative Example6 was 100. A smaller index indicates better processability.

(Evaluation 2) Viscoelasticity Parameter

A viscoelasticity testing machine “ARES” manufactured by RheometricScientific, Inc. was used to measure a viscoelasticity parameter in atorsion mode. Each measurement value was shown as an index obtainedassuming that a result obtained by the rubber composition of ComparativeExample 6 was 100. A tan 8 measured at 0° C. at a frequency of 10 Hz andstrain of 1% was used as an index of wet grip performance. A largerindex indicates better wet grip performance. Besides, a tan 8 measuredat 50° C. at a frequency of 10 Hz and strain of 3% was used as an indexof fuel efficiency. A smaller index indicates higher fuel efficiency.

(Evaluation 3) Tensile Strength and Tensile Elongation

Tensile strength and tensile elongation were measured in accordance witha tensile test method according to JIS K6251, and were shown as indexesobtained assuming that results of Comparative Example 6 were 100. Alarger index indicates better tensile strength and tensile elongation.

(Evaluation 4) Abrasion Resistance

An Acron abrasion tester (manufactured by Yasuda Seiki Seisakusho, Ltd.)was used to measure an abrasion amount through 1000 rotations at a loadof 44.4 N in accordance with JIS K6264-2, and results were shown asindexes obtained assuming that a result of Comparative Example 6 was100. A larger index indicates better abrasion resistance.

TABLE 4 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple21 ple 22 ple 23 ple 24 ple 25 ple 26 ple 27 ple 28 ple 29 ple 30Modified Diene-based Polymer (Sample No.) 1 2 3 4 5 6 7 8 9 10 (PhysicalProperty 5) Mooney Viscosity of 83 83 83 82 79 84 82 81 84 82 ModifiedDiene-based Polymer (100° C.) (Evaluation 1) Mooney Viscosity ofCompound index 83 85 80 78 84 85 78 78 78 78 (130° C.) Physical(Evaluation 2) tanδ at 50° C. index 80 75 70 73 82 83 73 73 75 77Properties (strain 3%) of (Evaluation 2) tanδ at 0° C. index 120 125 130128 115 120 128 124 120 121 Vulcani- (strain 1%) zate (Evaluation 3)Tensile Strength index 110 125 130 140 109 125 130 143 150 155(Evaluation 3) Tensile Elongation index 120 130 140 145 122 130 145 150151 151 (Evaluation 4) Abrasion Resistance index 125 130 140 150 123 130145 160 162 165

TABLE 5 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple31 ple 32 ple 33 ple 34 ple 35 ple 36 ple 37 ple 38 ple 39 ple 40Modified Diene-based Polymer (Sample No.) 11 12 13 14 15 16 17 18 19 20(Physical Property 5) Mooney Viscosity of 82 83 84 83 83 83 87 90 92 90Modified Diene-based Polymer (100° C.) (Evaluation 1) Mooney Viscosityof Compound index 89 87 82 86 85 80 82 72 68 100 (130° C.) Physical(Evaluation 2) tanδ at 50° C. index 85 80 75 80 75 70 70 83 85 83Properties (strain 3%) of (Evaluation 2) tanδ at 0° C. index 115 120 125120 125 130 130 115 110 120 Vulcani- (strain 1%) zate (Evaluation 3)Tensile Strength index 110 120 125 110 125 130 110 150 160 120(Evaluation 3) Tensile Elongation index 119 130 140 120 130 140 120 149166 107 (Evaluation 4) Abrasion Resistance index 124 130 140 125 130 140130 155 160 120

TABLE 6 Comparative Comparative Comparative Comparative ComparativeExample 6 Example 7 Example 8 Example 10 Example 11 Modified Diene-basedPolymer (Sample No.) 21 22 23 24 25 (Physical Property 5) MooneyViscosity of Modified Diene-based 75 83 96 96 90 Polymer (100° C.)(Evaluation 1) Mooney Viscosity of Compound (130° C.) index 100 98 94 40101 Physical (Evaluation 2) tanδ at 50° C. (strain 3%) index 100 90 8570 102 Properties of (Evaluation 2) tanδ at 0° C. (strain 1%) index 100103 109 109 100 Vulcanizate (Evaluation 3) Tensile Strength index 100 9590 78 100 (Evaluation 3) Tensile Elongation index 100 98 92 77 105(Evaluation 4) Abrasion Resistance index 100 110 115 76 105

As shown in Tables 4 to 6, it was confirmed that Examples 21 to 40 areexcellent in balance between wet skid resistance and a low hysteresisloss property when in the form of a vulcanizate, and also excellent inabrasion resistance as compared with Comparative Examples 6 to 11.

It was also confirmed that they have such a low Mooney viscosity of thecompound when in the form of a vulcanizate that good processability canbe exhibited.

It was also confirmed that they have practically sufficient fracturestrength when in the form of a vulcanizate.

This application is based upon the prior Japanese patent application(Japanese Patent Application No. 2018-188604), filed to the JapanesePatent Office on Oct. 3, 2018, the entire contents of which areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

A conjugated diene-based polymer of the present invention isindustrially applicable as a material or the like of tire treads,interiors/exteriors of vehicles, anti-vibration rubbers, belts, shoes,foam bodies, and various industrial products.

1. A conjugated diene-based polymer having an absolute molecular weightmeasured by viscosity detector-equipped GPC-light scatteringmeasurement, of 100×10⁴ or more and 5000×10⁴ or less, and having abranching number (Bn) measured by the viscosity detector-equippedGPC-light scattering measurement, of 8 or more.
 2. The conjugateddiene-based polymer according to claim 1, having a modification ratio of60% by mass or more.
 3. The conjugated diene-based polymer according toclaim 1, wherein the conjugated diene-based polymer is a conjugateddiene-based polymer having a star polymer structure having 3 or morebranches, wherein at least one branched chain of the star structurecomprises a portion derived from a vinyl-based monomer containing analkoxysilyl group or a halosilyl group, and the portion derived from thevinyl-based monomer containing an alkoxysilyl group or a halosilyl groupfurther comprises a main chain branch structure.
 4. The conjugateddiene-based polymer according to claim 1, wherein the portion derivedfrom the vinyl-based monomer containing an alkoxysilyl group or ahalosilyl group is a monomer unit based on a compound represented by thefollowing formula (1) or (2), and contains a branch point of a polymerchain containing the monomer unit based on the compound represented bythe formula (1) or (2), and at least one end of the conjugateddiene-based polymer is coupled by using a coupling agent:

wherein in the formula (1), R¹ represents a hydrogen atom, an alkylgroup having 1 to 20 carbon atoms, or an aryl group having 6 to 20carbon atoms, and may have a branch structure in a part thereof; R² andR³ each independently represent an alkyl group having 1 to 20 carbonatoms, or an aryl group having 6 to 20 carbon atoms, and may have abranch structure in a part thereof; each of R¹ to R³, if present in aplural number, is respectively independent; X¹ represents an independenthalogen atom; m represents an integer of 0 to 2, n represents an integerof 0 to 3, I represents an integer of 0 to 3, and (m+n+I) is 3; in theformula (2), R² to R⁵ each independently represent an alkyl group having1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, andmay have a branch structure in a part thereof, and each of R² to R⁵, ifpresent in a plural number, is respectively independent; X² and X³represent an independent halogen atom; m represents an integer of 0 to2, n represents an integer of 0 to 3, I represents an integer of 0 to 3,and (m+n+I) is 3; and a represents an integer of 0 to 2, b represents aninteger of 0 to 3, c represents an integer of 0 to 3, and (a+b+c) is 3.5. The conjugated diene-based polymer according to claim 4, containing amonomer unit based on a compound represented by the formula (1) whereinR¹ is a hydrogen atom, and m is
 0. 6. The conjugated diene-based polymeraccording to claim 4, containing a monomer unit based on a compoundrepresented by the formula (2) wherein m is 0 and b is
 0. 7. Theconjugated diene-based polymer according to claim 4, containing amonomer unit based on a compound represented by the formula (1) whereinR¹ is a hydrogen atom, m is 0, and I is
 0. 8. The conjugated diene-basedpolymer according to claim 4, containing a monomer unit based on acompound represented by the formula (2) wherein m is 0, I is 0, a is 0,and b is
 0. 9. The conjugated diene-based polymer according to claim 4,containing a monomer unit based on a compound represented by the formula(1) wherein R¹ is a hydrogen atom, I is 0, and n is
 3. 10. A branchingagent for the conjugated diene-based polymer according to claim 4,wherein the branching agent is a compound represented by the followingformula (1) or (2):

wherein in the formula (1), R¹ represents a hydrogen atom, an alkylgroup having 1 to 20 carbon atoms, or an aryl group having 6 to 20carbon atoms, and may have a branch structure in a part thereof; R² andR³ each independently represent an alkyl group having 1 to 20 carbonatoms, or an aryl group having 6 to 20 carbon atoms, and may have abranch structure in a part thereof; each of R¹ to R³, if present in aplural number, is respectively independent; X1 represents an independenthalogen atom; m represents an integer of 0 to 2, n represents an integerof 0 to 3, I represents an integer of 0 to 3, and (m+n+I) is 3; in theformula (2), R² to R⁵ each independently represent an alkyl group having1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, andmay have a branch structure in a part thereof, and each of R² to R⁵, ifpresent in a plural number, is respectively independent; X² and X³represent an independent halogen atom; m represents an integer of 0 to2, n represents an integer of 0 to 3, I represents an integer of 0 to 3,and (m+n+I) is 3; and a represents an integer of 0 to 2, b represents aninteger of 0 to 3, c represents an integer of 0 to 3, and (a+b+c) is 3.11. The branching agent according to claim 10, wherein the branchingagent is a compound represented by the formula (1) wherein R¹ is ahydrogen atom and m is
 0. 12. The branching agent according to claim 10,wherein the branching agent is a compound represented by the formula (2)wherein m is 0, and b is
 0. 13. The branching agent according to claim10, wherein the branching agent is a compound represented by the formula(1) wherein R¹ is a hydrogen atom, m is 0, and I is
 0. 14. The branchingagent according to claim 10, wherein the branching agent is a compoundrepresented by the formula (2) wherein m is 0, I is 0, a is 0, and b is0.
 15. The branching agent according to claim 10, wherein the branchingagent is a compound represented by the formula (1) wherein R¹ is ahydrogen atom, I is 0, and n is
 3. 16. An extended conjugateddiene-based polymer comprising: 100 parts by mass of the conjugateddiene-based polymer according to claim 1; and 1 to 60 parts by mass ofat least one selected from the group consisting of an extender oil, aliquid rubber, and a resin.
 17. A rubber composition comprising: arubber component; and 5.0 parts by mass or more and 150 parts by mass orless of a filler based on 100 parts by mass of the rubber component,wherein the rubber component contains, based on a total amount of therubber component, 10% by mass or more of the conjugated diene-basedpolymer according to claim
 1. 18. A tire comprising the rubbercomposition according to claim 17.